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 California Division of Alines 
 Special Report 56 
 
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 UNIVERSITY Or CALIFORNIA 
 DAVIS 
 
 NOV % 1959 
 LldHARY 
 
Digitized by the Internet Archive 
 
 in 2012 with funding from 
 
 University of California, Davis Libraries 
 
 http://archive.org/details/franciscancherti56gold 
 
GEOLOGY AND ECONOMIC POSSIBILITIES 
 OF THE LIMESTONE AND DOLOMITE DEPOSITS 
 OF THE NORTHERN GABILAN RANGE, CALIFORNIA 
 
 By OLIVER E. BOWEN, JR. and CLIFFTON H. GRAY, JR. 
 
 Mining Geologists, California Division of Mines 
 
 Special Report 56 
 
 CALIFORNIA DIVISION OF MINES 
 
 FERRY BUILDING, SAN FRANCISCO, 1959 
 
 
STATE OF CALIFORNIA 
 
 EDMUND G. BROWN, Governor 
 
 DEPARTMENT OF NATURAL RESOURCES 
 
 tDeWITT NELSON, Director 
 DIVISION OF MINES 
 GORDON B. OAKESHOTT, Chief 
 
 Special Report 56 
 Price 50£ 
 
CONTENTS Page 
 
 Abstract 5 
 
 Introduction n 
 
 General geology jq 
 
 Sur series jj 
 
 Quartz monzonite and granodiorite 13 
 
 Other granitic rocks 15 
 
 Vaqueros group and associated Tertiary rocks 15 
 
 Rock units mapped in detail in the Fremont Peak vicinity 16 
 
 Sequence and structure in the Fremont Peak rocks 19 
 
 Sur series section 19 
 
 Rocky Ridge fault zone 21 
 
 Field features useful in estimating the economic possibilities of the carbonate-rock masses— 21 
 
 Economic possibilities of limestone and dolomite deposits 23 
 
 Los Vergeles district 23 
 
 San Juan Canyon district 23 
 
 Barbee Ranch deposits 23 
 
 Bryan and Pearee-Twohy deposits 23 
 
 Flint-Steinbeck deposit 25 
 
 Harmony Hills deposit 25 
 
 Underwood deposits 25 
 
 Natividad district 25 
 
 Kaiser Aluminum and Chemical Company deposits 25 
 
 Porter dolomite deposit 28 
 
 Sugarloaf deposits 28 
 
 Other deposits 28 
 
 Fremont Peak district 28 
 
 Bardin Ranch deposits on Rocky Ridge 28 
 
 East Gabilan deposit 28 
 
 Fremont Peak deposits 31 
 
 Bird Creek district 31 
 
 A. S. and R. deposit 31 
 
 Bird Canyon Ledge 31 
 
 Middle Dam deposit 32 
 
 Power line deposits 32 
 
 Upper Bird Creek deposit 32 
 
 Cienega- Vineyard district 33 
 
 Garner-Harris deposits 33 
 
 Kaiser-Harris (Permanente) dolomite deposit 35 
 
 Martin Ranch deposits 35 
 
 McCray Ranch deposits 35 
 
 Palmtag-Harris deposits 36 
 
 Reeves North deposits 36 
 
 Westvaco (O'Hara Ranch) deposit 37 
 
 Hartnell district 37 
 
 Bluerock Mountain-Quail Creek deposits 37 
 
 Mount Hanlan-McPhails Peak district 37 
 
 Cowell-Thompson Creek deposit . 37 
 
 Hamilton, Harlan, Mayries, and McPhail deposits 38 
 
 Westphal Ranch deposits 38 
 
 Willow Creek district 39 
 
 Barite deposits west of Fremont Peak 39 
 
 References 40 
 
 (3) 
 
Illustrations Page 
 
 Plate 1. Geologic map and structure section of Fremont Peak area, Monterey and San 
 
 Benito Counties, California In pocket 
 
 Figure 1. Index map of the northern Gabilan Range showing area mapped (shaded) 
 
 and topographic maps covering area 7 
 
 Figure 2. Regional geologic map of northern Gabilan Range 10 
 
 Figure 3. Generalized columnar section, northern Gabilan Range 11 
 
 Figure 4. Map showing location of limestone and dolomite deposits, Fremont Peak area 22 
 
 (Photos by Mary Hill) 
 Frontispiece. Fremont Peak from the west 6 
 
 Photo 1. Fremont Peak from the east 8 
 
 2. Rocky Ridge, Fremont Peak in background 9 
 
 3. Fremont Peak from the southeast 9 
 
 4. Panorama across Salinas Valley 12 
 
 5. Rolling late Tertiary surface south of Fremont Peak 14 
 
 6. Pinecate sandstone near Ideal cement plant 14 
 
 7. Vaqueros limestone conglomerate 15 
 
 8. Steep-dipping limestone beds, Fremont Peak road 16 
 
 9. Limestone outcrop, south slope of Fremont Peak 16 
 
 10. Detail of solution pits in limestone 16 
 
 11. Closeup of coarsely crystalline limestone 16 
 
 12. Large solution pits in cavernous limestone 17 
 
 13. Hackly weathered surface of siliceous limestone 17 
 
 14. Elephant-skin texture on dolomite, Sugarloaf 17 
 
 15. Etched joint pattern in dolomite, Sugarloaf 17 
 
 16. Banded assemblage of mixed carbonate rocks, Fremont Peak 18 
 
 17. Detail of banded carbonate rock 18 
 
 18. Quartzite hill east of park headquarters 19 
 
 19. Hackly, lichen-covered surfaces of replacement quartz, east of park headquarters 20 
 
 20. Ideal cement plant near San Juan Bautista 24 
 
 21. Ideal Cement Company quarries 24 
 
 22. Kaiser Aluminum and Chemical Co. plant (photo by Cat Pictures) 26 
 
 23. Quarries and dumps at Natividad 27 
 
 24. Quarry face and floor, Natividad 27 
 
 25. Granite dikes in dolomite, Natividad 28 
 
 26. Initial stage in exploration of dolomite deposit on Reeves Ranch 29 
 
 27. Closer view of drill rig shown in photo 26 29 
 
 28. Bouldery limestone outcrops, power line deposits 30 
 
 29. Westvaco operation near Vineyard winery 33 
 
 30. Westvaco 's crushing and sizing installation 34 
 
 31. Quarry benches in white dolomite, Westvaco 35 
 
 32. Closeup of quarry-run dolomite, Westvaco 36 
 
 33. Old lime kilns at Cowell-Thompson Creek deposit 38 
 
 34. Rocky Ridge, barite dumps 39 
 
 35. Closeup of barite veins in Rocky Ridge 40 
 
 (4) 
 
ABSTRACT 
 
 Deposits of limestone and dolomite in the northern Gabilan Range have become 
 important sources of raw materials for San Francisco Bay area industries, supplying 
 one cement plant and three magnesia refractory and chemical plants. The deposits 
 are chiefly in the crystalline basement complex of the range, as pendants suspended 
 in granitic rocks and schist. Some of the pendants contain masses of limestone and 
 dolomite of commercial size and purity, whereas others contain mixed calcitic and 
 dolomitic rocks of no present economic importance. Criteria useful in recognizing calcitic 
 and dolomitic rocks in the Fremont Peak vicinity are grain relief, grain size and grain 
 color, as seen on weathered surfaces, and the disposition of solution pits. The more 
 siliceous varieties of carbonate rock are also likely to be magnesian. 
 
 The major rock units of interest in the area are the metamorphosed Sur series of 
 probable Paleozoic age, undivided granitic rocks of Jura-Cretaceous age, and the 
 Vaqueros group of lower Miocene age. Carbonate rocks of potential commercial impor- 
 tance are found in both the Sur series and the conglomerate portions of the Vaqueros 
 group. Quartz monzonite and granodiorite predominate among the granitic rocks. 
 Sur series rocks, in descending order of abundance, are quartz-mica schist, limestone, 
 dolomite, and quartzite. An upper and lower schist member and a middle carbonate-and- 
 schist member are recognized. Subunits mapped for economic purposes in the Fremont 
 Peak vicinity are: limestone; dolomite; limestone with granitic rock and schist intercala- 
 tions; mixed limestone and dolomite; siliceous limestone; limy, siliceous dolomite,- gray 
 replacement quartz; quartz-mica schist; pink quartzite; mixed schist and granitic rocks; 
 and quartz monzonite-granodiorite. Vein and replacement masses of barite are found in 
 the carbonate rocks west of Fremont Peak. 
 
 (5) 
 

GEOLOGY AND ECONOMIC POSSIBILITIES OF THE LIMESTONE AND 
 DOLOMITE DEPOSITS OF THE NORTHERN GABILAN RANGE, CALIFORNIA 
 
 By OLIVER E. BOWEN, JR. and CLIFFTON H. GRAY, JR. 
 
 INTRODUCTION 
 
 Purpose of the Study. In recent years there has been 
 increasing- interest in both the limestone and dolomite 
 leposits of the northern Gabilan Range because of their 
 jroximity to markets and to heavy transportation. Up 
 ;o the time of the present study no detailed work had 
 )een done on the carbonate rocks and only two parts of 
 ;he northern Gabilan Range had been mapped in which 
 he carbonate rocks were even roughly delineated. So far 
 is the authors know, this study is the first attempt made 
 n this vicinity to separate limestone and dolomite masses 
 nto mapping units. The present study was instigated 
 vith three objectives: (1) for the purpose of gaining 
 itratigraphic information on the Sur series — the ancient 
 netasedimentary sequence which contains the carbonate 
 ■ocks; (2) to find out possible geologic controls over the 
 listributions of limestone and dolomite deposits in the 
 Jabilan Range; (3) and to map in greater detail than 
 leretofore the carbonate-rock masses in the Fremont 
 *eak vicinity. The Fremont Peak vicinity was chosen 
 or study because there the Sur series appears to be more 
 learly intact, stratigraphically, and exposures are 
 letter there than in other parts of the Gabilan Range. 
 Phe detailed geologic map of the Fremont Peak vicinity 
 ras completed in the fall of 195-4 and rechecked in the 
 all of 1957. Work on the individual deposits extended 
 rom 1954 to late 1957. The data presented are complete 
 o January 1, 1958. 
 
 This paper describes in some detail the geology of 8 
 quare miles of terrain in the vicinity of Fremont Peak. 
 t also includes a discussion of the general geologic 
 eatures of the northern Gabilan Range, together with 
 
 generalized small-scale geologic map. Most of the 
 lasses of carbonate rock in the northern Gabilan Range 
 re discussed with regard to their geology and economic 
 tossibilities ; deposits of Los Vergeles, San Juan Canyon, 
 Jatividad, Fremont Peak, Bird Creek, Cienega-Vine- 
 ard, Hartnell, Mount Harlon-McPhails Peak, and Wil- 
 aw Creek districts are tabulated, described briefly, and 
 valuated. 
 
 Mapping was done on U. S. Department of Agriculture 
 holographs, series ABO-BUX, on a scale of 1:10,000. 
 'he geology was transferred from this to a composite 
 opographic base derived from the new Hollister and 
 Ian Juan Bautista 7^-minute sheets and the Gonzales 
 5-minute sheet of the U. S. Geological Survey. 
 
 -SANTA- 
 
 ^S 
 
 CRUZ "N 
 
 SANTA 
 
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 A/^x/ 
 
 / 
 
 X 
 
 
 Salinas 
 
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 Figure 1. Index map of the northern Gahilan Range showing 
 area mapped (shaded), and topographic maps covering the area. 
 
 A total of 97 samples were collected by the authors for 
 analysis. Fifty-six of these were analyzed by Abbot A. 
 Hanks, Inc., of San Francisco, and the remainder by 
 L. A. Caetano of the San Juan Bautista plant of Ideal 
 Cement Company. In addition, the Ideal Cement Com- 
 pany made 444 analyses, done in former years on ma- 
 terial on the Bryan, Pearce-Twohy, Underwood, and 
 Barbee deposits, available to the authors. These 541 
 analyses are the bases upon which the probable economic 
 worth of the various deposits was determined. 
 
 Location and Accessibility. The area studied in detail 
 is a rectangular strip about 5 miles long and 14. miles 
 wide oriented along the crest of the Gabilan Range. Fre- 
 mont Peak, also called Gabilan Peak, the highest in the 
 vicinity at 3,171 feet, is the approximate center of the 
 area. Fremont Peak lies (\\ airline miles south of San 
 Juan Bautista or about 80 miles southeast of San Fran- 
 cisco. Most of the plot mapped is in Monterey County — 
 but the northern and eastern margins are in San Benito 
 County. The district is readily accessible to wheeled 
 vehicles by the paved Fremont Peak State Park road, 
 although present grades and curves are not favorable to 
 heavy trucking. The peak is about 11 miles by road from 
 
 (7) 
 
CALIFORNIA DIVISION OF MINES 
 
 [Special Report 5 
 
 p -: 
 
 - 
 
 J> :'' r Sfr ^*£» 
 
 
 Photo 1. 
 
 Fremont Peak from the east. The twin peaks are surmounted by partly silicified dolomitic limestone. A tongue of schist 
 
 occupies the saddle. 
 
 San Juan Bautista. Several dirt roads connect with the 
 Fremont Peak road. All of the area mapped except the 
 State Park is privately owned ranch land not open to 
 public entry; nor may mineral locations be made in the 
 park. 
 
 Physical Features. The Gabilan Range, one of the 
 prominent topographic features of the central Coast 
 Ranges, is essentially a horst or fault-block range made 
 up predominantly of pre-Tertiary crystalline rocks. The 
 deeply alluviated Salinas and San Juan-San Benito River 
 Valleys form, respectively, its west and east limits. Over 
 much of its length the range is bordered on the east by 
 the San Andreas fault zone. Rising abruptly from local 
 base level at an elevation of 200 feet, the mountains gain 
 heights exceeding 3,700 feet. The surface has been deeply 
 dissected along the flanks of the range and along north- 
 west-trending faults, but parts of a late Tertiary or early 
 Quaternary mature surface yield some gently rolling 
 laud along the range crest — such as the land southeast 
 of Fremont Peak. 
 
 As fairly homogeneous granitic rocks underlie much 
 of the range, the drainage pattern developed is largely 
 dendritic; but locally, trellis drainage has developed 
 along fault zones. The main drainage south of the ridge 
 surmounted by Fremont Peak is into Gabilan Creek; 
 the arc;) to the northwest is drained by its main tribu- 
 tary. Mud Creek. Both drain into Salinas Valley. Bird 
 Creek and its tributaries drain the northeast part of the 
 area and ultimately join the San Benito River. 
 
 The climate in the Gabilan Range is of Mediterranear 
 type, with summer fogs and winter rainfall, which aver 
 ages about 20 inches. Temperatures fall below freezing 
 for short periods during the winter months and reach 
 80 to 100 degrees in summer. 
 
 Previous Gedtogic Work. No previous work has cov-; 
 ered the Gabilan Range or the Fremont Peak area in 
 detail. Several published reports include the Gabilan 
 Range or parts thereof but do not deal specifically with 
 carbonate rocks of the Fremont Peak area. J. D. Whit- 
 ney, in 1865, gave the first geologic description of this 
 region in Volume I of the Geological Survey of Cali- 
 fornia. He described the rock types present but named 
 no formations. In 1888 George F. Becker commented on 
 some of the general features of the Gabilan Range and 
 was the first to call the carbonate rocks the "Gabilan 
 limestone". The first complete report published, which 
 covered part of the Fremont Peak vicinity, was by J. E. 
 Allen (1946) on the geology of San Juan Bautista quad- 
 rangle ; it includes a geologic map on a scale of 1 : 62,500. 
 Taliaferro (1948) published a geologic map of Hollister 
 quadrangle on the same scale. These two maps include 
 most of the area of the present study. Unpublished work 
 includes maps of the Bird Canyon and East Gabilan 
 limestone deposits made by Bailey and Robin Willis in 
 1925, and lists of chemical analyses of samples collected 
 at various times by Pacific Portland Cement Company. 
 
 Acknowledgments. The authors wish to express their 
 appreciation to John A. Wolfe, W. E. Brown, and Leon- 
 
1591 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 **te* 
 
 *-4.J$.'4\ 
 
 
 ^* • "/. 
 
 
 Photo 2. Rocky Ridge terminated in the background by the twin peaks of Fremont Peak, observer facing east. White 
 dumps of the barite workings are prominent in the middle ground. The crest of Rocky Ridge is marked by a spine of dolomitic, 
 partly silicified, partly brecciated limestone. This is the edge of a steeply south-dipping, sheet-like mass projecting irregularly 
 downward into a sea of granitic rock and schist much like the roots of a row of teeth. A tunnel driven through the ridge 
 500 feet below the crest would in many places be entirely within granite and schist. 
 
 ')., 
 
 lag 1 * * 
 
 - ~\ 
 
 
 Photo 3 Fremont Peak as seen from the southeast. The two brush-accented belts of carbonate rock and the dividing 
 schist tongue that crosses the saddle can easily be seen. The foreground rocks are quartz replacements of dolomitic lime- 
 stone a gray cavernous quartzite. The silica was probably introduced at the time of intrusion of the granitic rocks. 
 
10 
 
 CALIFORNIA DIVISION OF MINES 
 
 [Special Report 5( 
 
 A N A T I ON 
 
 River terrace 
 •9t.i de po s i l s. 
 
 Gravels and 
 e d sands. 
 
 | P j Pur i s i m a group 
 M\? I Volcanic rocKs. 
 
 TI2S 
 
 T I3S 
 
 SALI N AS 
 
 T I4S 
 
 T I5S 
 
 R 3 E 
 
 R 4 E R5E R6E 
 
 Figure 2. Regional geologic map of northern Gabilan Range. 
 
 R 7E 
 
 ard Caetano of Ideal Cement Company, and L. N. Bry- 
 ant, formerly of the Ideal Cement Company, whose 
 cooperation made this study possible. The willing co- 
 operation of the owners of the Reeves and Crowe-Harris 
 Ranches in allowing the writers access to their lands is 
 gratefully acknowledged. Howard Harris provided much 
 valuable information on the terrian and outcrops south- 
 cast of Fremont (Gabilan) Peak. The park rangers of 
 the State Division of Beaches and Parks at Fremont 
 Peak State Park helped the authors in many ways dur- 
 ing tlic course of field work. 
 
 T. C. Sersen, John A. Wolfe, W. A. Young, R. F. 
 Moran, Howard Harris, and Ivan Hall all read and 
 criticized the manuscript or parts thereof. Their assist- 
 ance is greatly appreciated. 
 
 The excellent photo coverage was the work of Mary 
 Hill and Elisabeth Egenhoff of the Division of Mines 
 editorial staff. 
 
 GENERAL GEOLOGY 
 
 Rocks of the northern Gabilan Rang'.' are predom- 
 inantly biotite quart/, monzonite and associated granitic 
 intrusives — most probably of Late Jurassic or Early Cre- 
 s age. Suspended in these granitic rocks are pend- 
 3 Of strongly metamorphosed sedimentary rocks of 
 
 probable Paleozoic age among which mica schist, lime- 
 stone, dolomite, and quartzite are the principal types. 
 Many of the metasedimentary pendants are aligned in 
 an easterly direction whereas the axis of the range 
 trends northwest. Along the northeast margin of the 
 range in the vicinity of San Juan Bautista is a succes- 
 sion of clastic marine sediments and andesitic volcanic 
 rocks of Tertiary age that has been strongly folded and 
 faulted, but almost everywhere this group of rocks is 
 in fault contact with the crystalline basement rocks 
 previously mentioned. Miocene ( ?) rhyolite, both intru- 
 sive and extrusive, is exposed in the southern part of the 
 Gabilan Range but is not found within the limits of this 
 study. 
 
 The metasediments have been correlated with the Sur 
 series of the Santa Lucia Mountains and Sierra de Salinas 
 by several previous authors, and evidence uncovered dur- 
 ing this investigation is not in conflict with this thesis. 
 The carbonate rocks of the sequence, even though they 
 appear at numerous horizons in the Sur sequence, were 
 lumped together and called "Gabilan limestone" by 
 Becker (1888) and Trask (1926). The schists and quartz- 
 ites have been lumped together as "Sur schist" by many 
 California geologists. Inasmuch as the names Gabilan 
 limestone and Sur schist have no real formational or 
 
1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 11 
 
 Figure 3. Generalized columnar section, northern Gabilan 
 Range. In part after Allen, 1946, p. 18. 
 
 stratigraphic significance, they will not be used in this 
 study, and the less specific term "Sur series" will be 
 used for the entire metasedimentary sequence. 
 
 Sur Series 
 
 The Sur series of the Santa Lucia Mountains has been 
 described at length by Trask (1926) and Reiche (1937). 
 Reiehe in particular lists many petrographic data on 
 rocks of the series. Neither author, however, names a 
 type locality or describes a typical sequence in the 
 series. Because of great elongation and distortion of 
 the beds during metamorphism, identification of tops 
 and bottoms of beds has been rendered virtually im- 
 possible. Consequently, both Trask 's and Reiche 's esti- 
 mates of thickness of the series are based on an assumed 
 homoclinal attitude whereas they recognize the possibil- 
 ity of repetition by both folding and faulting. Trask 
 estimates the thickness of the series on Point Sur quad- 
 rangle to be in excess of 5,000 feet. Reiche recognizes a 
 possible thickness of 10,000 feet for the series in Lucia 
 quadrangle and describes the carbonate rocks as "nu- 
 merous layers — intercalated in the schist". 
 
 In the most nearly complete section in the vicinity 
 of Fremont Peak the Sur series has a thickness of at 
 least 8,000 feet, if a homocline dipping north is assumed 
 and leaves of intercalated granitic rock are disregarded. 
 Both "upper" and "lower" contacts are against granite 
 intrusions, so that much of the sequence is probably 
 missing. Three crudely defined members are recognized : 
 an upper schist about 1,400 feet thick; a middle car- 
 bonate member about 3,400 feet thick, and a lower schist 
 member at least 3,500 feet thick. This section is described 
 in greater detail under Sequence and Structure. The 
 schist members both contain injections of granitic ma- 
 terial and have both been granitized to some extent — 
 that is, the original clastic material has been replaced 
 by rock of granitic character. Lenses of schist are in the 
 carbonate members and lenses of carbonate are in schist, 
 indicating that the original sedimentary sequence was 
 heterogeneous. Sheets and irregular masses of quartz 
 monzonite also intrude the carbonate rock masses as well 
 as the schist. 
 
 In previous works concerning the Sur series and Gab- 
 ilan limestone, no mention has been made of the presence 
 of dolomite in the carbonate rock masses, and it may be 
 that dolomite is rare in the Sur series of the Santa Lucia 
 Mountains. However, dolomite is present in the carbon- 
 ate rocks of the Sierra de Salinas and is an exceedingly 
 common rock type in the northern Gabilan Range. Be- 
 cause the distribution of limestone and dolomite is of 
 prime importance to manufacturers of cement, magne- 
 sium chemicals, and magnesium refractories, as well as to 
 many other consuming industries, particular attention 
 has been paid in this study to dolomite and dolomite- 
 rich rocks. 
 
 Dolomites are widely distributed among the many 
 carbonate-rock masses and are not found at any par- 
 ticular horizon or horizons. Where presence of bedding 
 planes can be determined the dolomite invariably trans- 
 gresses the bedding planes and nowhere is confined to 
 distinct beds. Contacts between dolomite and calcite 
 rocks as a rule are complex, with feathery and finger- 
 like salients of dolomite penetrating the adjacent calcite 
 rocks. These features suggest thai the dolomtie has come 
 
12 
 
 CALIFORNIA DIVISION OP MINES 
 
 [Special Report 
 
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1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 13 
 
 in as replacement of limestone and is not an original 
 constituent of sedimentation. 
 
 Dolomite rock in the Fremont Peak vicinity is readily 
 distinguishable from the adjacent limestone (caleite 
 rock) on weathered surfaces because of its finer grain 
 size, cream to pale buff color, and the character and 
 arrangement of solution pits. These differences are dis- 
 cussed in greater detail in later paragraphs. Graphite 
 flakes and dust-like inclusions of organic matter are 
 common in caleite rocks and rare in dolomite. 
 
 Medium-grained and fine-grained quartzite in pale 
 pink to pale red hues is present as non-persistent, len- 
 ticular beds in mica schist. The beds range from a few 
 inches to 2 or 3 feet in thickness, and there are grada- 
 tional facies between the quartzite and quartz-mica 
 schist. The texture of the quartzite and its relationship 
 to adjacent schist beds suggest that it was laid down as 
 sandstone interbedded with clay shale. 
 
 Another type of quartzite, in large masses in the Sur 
 series of the Fremont Peak vicinity, is clearly of replace- 
 ment origin. This rock is light dull gray in hand speci- 
 men or on weathered surfaces, and has numerous vugs 
 lined with small quartz crystals. It is found in or adja- 
 cent to masses of carbonate rock, and commonly includes 
 small, relict patches of the limestone it has replaced. 
 Quartzite of this type forms most of the ridge top east 
 of the Fremont Peak Park headquarters and is also 
 found extensively in the Bird Canyon limestone deposit 
 and along Rocky Ridge west of Fremont Peak. 
 
 Vein and replacement masses of coarse-grained, light- 
 gray and white barite are also found along Rocky Ridge 
 west of Fremont Peak. These closely resemble the coars- 
 er-grained facies of limestone and are distinguished 
 chiefly by the much greater weight of the barite rock. 
 Barite has been mined from time to time in the Fremont 
 Peak vicinity. 
 
 The greatest bulk of rock in the Sur series is quartz- 
 mica schist and gneiss. The principal minerals are 
 quartz, biotite, and muscovite ; plagioclase, orthoclase, 
 andalusite or sillimanite, and garnet are present in 
 minor amounts. Biotite predominates in the dark bands 
 and quartz in the light bands. Lime silicate minerals 
 such as diopside, wollastonite, and tremolite have devel- 
 oped where the original shales were limy. The mica 
 schists are gradational into gneissoid and normal quartz 
 monzonite and granodiorite, and granitic rocks and their 
 aplitic satellites intimately invade the schist sequences in 
 many localities. 
 
 A mass of calc-silicate hornfels crops out over several 
 acres on the southeast slope of Fremont Peak. The rock 
 is dense, microcrystalline, and greenish black on fresh 
 surfaces, but weathers to a rusty brown. It occurs along 
 the border of a pendant of carbonate-rock, chiefly 
 dolomitic limestone, and has formed by contact meta- 
 morphism of such magnesian limestone. Under the 
 microscope the rock is a mosaic of crystals of tremolite, 
 wollastonite, diopside, magnetite, and green spinel, with 
 scattered clots of biotite and andalusite and a few 
 patches of late-formed chlorite and pyrite. 
 
 Garnet-epidote tactite showing a little scheelite is in 
 sparse, small patches west of the barite prospects; but 
 elsewhere garnet-bearing contact-metamorphic rocks are 
 absent, or developed only in very small patches. 
 
 Age and Correlation. No precise age-determining 
 features were found in any of the Sur series rocks, but 
 they clearly arc older than the -Jura-Cretaceous granitic 
 rocks which have intruded them (see under quartz, mon- 
 zonite and granodiorite). Indistinct forms suggestive of 
 cup corals were found at several places along the ridge 
 crest west of Fremont Peak and rocks suggestive of 
 erinoidal calcarenites were observed in the same general 
 vicinity. The series is similar to many metamorphosed 
 late Paleozoic and early Mesozoic successions in the 
 southern Sierra Nevada and Tehachapi Mountains. 
 
 Quartz Monzonite and Granodiorite 
 
 Lawson (1893) first applied the name "Santa Lucia 
 granite" to the plutonic intrusives in the vicinity of Car- 
 mel Bay. In todays nomenclature, Lawsons' "granite" 
 is a biotite granodiorite, inasmuch as the average com- 
 position is 30-35 percent quartz, 20-25 percent orthoclase, 
 35-45 percent oligoclase and 3-7 percent biotite. Trask 
 (1926) correlated the plutonic rocks of Point Sur quad- 
 rangle with those of Lawson and designated them col- 
 lectively as the "Santa Lucia quartz diorite. " Trask, 
 however, recognized facies ranging from quartz diorite 
 to granite. Reiche (1937) recognized both granite and 
 quartz diorite in the Lucia quadrangle but attached no 
 place names to them. Andrews (1936) adopted Lawson 's 
 name Santa Lucia "granite" for the group of plutonic 
 rocks in the southern Gabilan Range but recognized 
 numerous facies ranging from soda granite to quartz 
 diorite. 
 
 The granitic rocks of the northern Gabilan Range 
 (particularly those in the Fremont Peak vicinity) are 
 principally quartz monzonite and granodiorite, quartz 
 monzonite predominating. Biotite is the common acces- 
 sory mineral although hornblende is locally abundant in 
 melanocratic segregations. The quartz content is uni- 
 versally high in all varieties; most commonly oligoclase 
 forms 35-40 percent of the quartz monzonite, perthitic 
 microcline 30-35 percent, and biotite 1 to 3 percent. In 
 the granodioritic facies, oligoclase or oligoclase-andesine 
 increases at the expense of microcline and the biotite 
 commonly increases to 5 percent or more. The prevailing 
 texture is coarse hypidiomorphic granular without the 
 conspicuous phenocrysts of orthoclase that typify the 
 granitic rocks farther west at Carmel Bay and Point 
 Lobos. Where the quartz monzonite is in contact with 
 quartz-mica schist it commonly grades subtly into gneiss- 
 oid or schistose facies in which biotite-rich bands are 
 developed parallel to the regional planarity of the schists. 
 This suggests partial regional granitization of the meta- 
 sedimentary sequence. In many places, however, the con- 
 tacts between granitic rocks and metasediments are 
 distinctly intrusive, the intruding rock showing evidence 
 of considerable fluidity. Although the granitic rocks 
 probably are susceptible to subdivision into at least two 
 mappable units in the Fremont Peak area, such subdivi- 
 sion has been beyond the scope of this work. 
 
 Age and Correlation. The granitic rocks are un- 
 doubtedly traceable southeastward to the Pinnacles vicin- 
 ity described by Andrews (1936) and although sepa- 
 rated from the basement complex of the Sierra de Salinas 
 and Santa Lucia Mountains by alluvial fill of the Salinas 
 Valley, there seems little doubt that the metasediments 
 
14 
 
 CALIFORNIA DIVISION OF MINES 
 
 [Special Report 5( 
 
 
 Photo 5. A view of one of the larger, gently rolling late Tertiary uplifted surfaces that forms the pasture land of the 
 Reeves Ranch ; observer facing southeast from Fremont Peak. 
 
 %r 
 
 COTO <i. A pair of strike ridges in the weather-resistant Pinecate sandstone member of the Oligocene San Lorenzo group 
 as seen in the vicinity of the Ideal cement plant at San Juan Bautista. 
 
1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 15 
 
 Photo 
 
 Reds of limestone conglomerate in the Vaqueros formation along the San Juan Grade ,'U miles by road south- 
 west of San Juan Bautista. 
 
 and granitic rocks of the northern Gabilan Range are 
 parts of the same sequence found in the Sierra de Salinas 
 ind Santa Lucia Mountains. Several age determinations 
 made upon granitic rock debris north and south of Mon- 
 terey Bay (Hutton, 1951; Curtis, et ah, 1956) have 
 shown them to be Middle to Late Cretaceous. Some of the 
 jranitic rocks of the Gabilan Range may be as old as 
 Upper Jurassic, but it is doubtful that any are older. 
 
 Other Granitic Rocks 
 
 Minor dikes and irregular intrusions of several other 
 types of granitic rocks cut the Sur series and the quartz 
 nonzonite in many places. Hornblende-biotite quartz 
 iiorite porphyry dikes cut dark hornfels and schist on 
 the south slope of Fremont Peak. In hand specimen the 
 porphyry shows euhedral hornblende crystals ranging 
 from I to 1 centimeter in longest dimension, together 
 frith smaller phenocrysts of biotite and feldspar. Most 
 )f the groundmass is indeterminate in hand specimen. 
 Under the microscope the rock is seen to be composed of 
 hornblende (40%), andesine (30%), quartz (15%), di- 
 jpside (15%), and biotite {1' ', ). 
 
 Pegmatite and aplite dikes a few inches to a foot or 
 two in thickness also cut the quartz monzonite-Sur series 
 ;omplex. These are mineralogically simple, consisting 
 dmost entirely of quartz, feldspar, and biotite. Ortho- 
 :lase or microcline generally predominates over oligo- 
 dase and the quartz content varies widely from place 
 to place even in the same dike. Muscovite is irregularly 
 aid sparsely distributed or absent. 
 
 Vaqueros Group and Associated Tertiary Rocks 
 
 The only Tertiary units in the northern Gabilan 
 Range that contain carbonate rocks of possible economic 
 significance are members of the lower Miocene Vaqueros 
 group. These have been described by Allen (1946). The 
 Vaqueros group is overlain by Miocene andesitic vol- 
 canic rocks and underlain by sandstone and siltstone of 
 the Oligocene San Lorenzo group. Vaqueros rocks crop 
 out discontinuously in a complexly folded and faulted 
 area of about 30 square miles in a northwest-trending, 
 arcuate patch centering 1] miles southwest of San Juan 
 Bautista. They are well exposed along the San Juan 
 grade, which roughly bisects the area of outcrops. Con- 
 glomerates, composed predominantly of limestone peb- 
 bles, cobbles, and boulders derived from the Sur scries, 
 form much of the lower part of the Vaqueros strati- 
 graphic sequence. Conglomerate members reach a thick- 
 ness of 500 feet and the total thickness of the group 
 ranges up to 1,800 feet (Allen, 1946, p. 28). Conglom- 
 erate masses are lenticular to irregular in form, having 
 been laid torrent ially in stream channels. They are inter- 
 bedded and interfingered with sandstone, conglomerate, 
 and sedimentary breccia having only a small proportion 
 of carbonate debris. 
 
 Because of the proximity of the portland cement plant 
 at San Juan Bautista, the Vaqueros limestone conglom- 
 erate is of potential use in portland cement. Insufficient 
 sampling has been done by the operating company 1o 
 establish the worth of these deposits as a supplemental 
 
16 
 
 CALIFORNIA DIVISION OF MINES 
 
 [Special Report 56 
 
 , 
 
 
 Photo 8. Steep-dipping beds of limestone along the Fremont 
 Teak road where it crosses Rocky Ridge just east of Fremont Peak. 
 The grass-covered depression between the limestone beds in the 
 center of the photo has developed by erosion of one of the less 
 resistant interleaved sheets of schist and granitic rock. 
 
 source of carbonate raw materials to extend the re- 
 serves of massive crystalline rocks in the plant vicinity. 
 Some of the conglomerate deposits lie within a mile of 
 the cement plant, but the extent to which these can be 
 used depends largely upon the proportion of dolomite 
 and magnesian limestone debris present (the MgO con- 
 tent in portland cement clinker must not exceed 5 per- 
 cent). As massive samples of mill-run proportions woidd 
 be necessary to adequately test the content of the con- 
 glomerates, such sampling and analytical work was not 
 attempted by the California Division of Mines. The 
 authors did note the presence of appreciable numbers of 
 dolomite and dolomitic limestone cobbles and pebbles in 
 several exposures of Vaqueros conglomerate near the 
 cement plant, so the magnesium content of the limestone 
 conglomerate would have to be carefully checked. 
 
 ROCK UNITS MAPPED IN DETAIL IN THE 
 FREMONT PEAK VICINITY 
 
 In preparing the geologic map of the Fremont Peak 
 vicinity, which accompanies this report, rock units were 
 chosen to bring out to best advantage the economic pos- 
 sibilities of the rocks of the area. Rock types that were 
 too intimately mixed for adequate representation on the 
 map scale adopted, or which were too intimately mixed 
 to allow selective mining of the constituent rock types, 
 were grouped together as a single unit. 
 
 Photo 9. A typical outcrop of limestone on the south slope of 
 Gabilan Peak showing the coarsely crystalline, complexly jointed, 
 partly brecciated character of the rock. Colors are white to blue- 
 gray. 
 
 
 Photo 10. Well-developed, sharp-edged, cup-like solution pits 
 in high-grade limestone. Compare these solution pits and the gen- 
 eral surface appearance with the dolomite surfaces shown in photos 
 14 and 15. 
 
 ^m 
 
 1 w-> 
 
 
 A 
 
 Photo 11. Closeup of a coarsely crystalline limestone surface 
 showing the well-etched cleavage surfaces of the individual crystals. 
 Most of the dolomites of the Fremont Peak vicinity are noticeably 
 finer grained. 
 
[959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 17 
 
 
 ; 7 . S^i 
 
 
 Photo 12. Large solution pits in cavernous limestone. In eon- 
 act with the limestone at the left side of the photo is a replace- 
 oent patch of dolomite which has no solution pits. 
 
 Photo 13. Typical hackly surfaces on siliceous limestone where 
 uartz and silicate minerals have developed in patches under influ- 
 nce of contact metamorphism. 
 
 Photo 14. Elephant-skin texture of weathered dolomite out- 
 rops on the southwest slope of Sugarloaf. Silver half-dollar gives 
 cale. Cup-shaped, sharp-edged solution pits are conspicuously 
 bsent as compared with the weathered limestone surfaces shown in 
 ihotos 10 and 12. 
 
 Limestone (Is)*. The material mapped as limestone 
 is uniform, high in calcium and low in magnesium, usa- 
 ble in portland cement, and in most cases, for numerous 
 other commercial purposes. Type samples were found to 
 contain less than 3 percent MgO and more than 94 per- 
 cent CaO. A number of samples ran as high as 98 percent 
 CaC0 3 . The iron oxide content of most samples falls 
 within the range 0.11 to 0.20 percent with a maximum 
 of about 0.50 percent Fe 2 3 . The limestone ranges from 
 medium-grained varieties having an average grain di- 
 ameter of about 1 mm to coarse-grained varieties aver- 
 aging more than 1 cm in diameter. Colors range from 
 dark blue-gray to white on fresh surfaces. No amorphous 
 or microcrystalline varieties were observed. 
 
 Photo 15. Etched joint pattern in medium to coarse-grained 
 dolomite on Sugarloaf, Natividad district. 
 
 Dolomite (do). The material mapped as dolomite 
 is uniform, of potential commercial quality, and has an 
 MgO content of more than 17 percent. In some places, 
 however, the iron content is too high for the rock to be 
 used for refractory purposes. Analyses show from 0.12 
 to 1.16 percent Fe 2 0-i content, with the mean at about 
 0.4 percent. Colors range from blue gray to creamy white 
 on fresh surfaces. No pure-white dolomite was observed 
 in the Fremont Peak vicinity. Rock having a high de- 
 gree of whiteness is present at Natividad, Monterey 
 County, and on the Crowe-Harris, Martin, Hamilton, 
 and intervening ranches on the southwest side of Cienega 
 Road in the Bird Creek- Vineyard district of San Benito 
 County. Dolomite in the Fremont Peak vicinity is fine 
 grained, in marked contrast to the medium and coarse- 
 grained limestones. It is also much finer grained than the 
 white dolomites of the Bird Canyon and Natividad dis- 
 tricts, and much of it will not disintegrate under cal- 
 cination. 
 
 Limestone and Dolomite (Isdo). The material mapped 
 as limestone and dolomite consists of limestone masses 
 having numerous replacement patches of dolomite. It is 
 by far the largest unit mapped insofar as areal extent is 
 concerned. The proportion of dolomite to limestone 
 varies from place to place but the authors doubt that 
 
 • Symbols "Is," "do," etc., which follow the unit names are used on 
 the accompanying geologic map. 
 
18 
 
 CALIFORNIA DIVISION OP MINES 
 
 [Special Report 56 
 
 * 
 
 • ! 
 
 K 
 
 a 
 
 
 Photo 1G. Banded assemblage of mixed carbonate rocks on the 
 south slope of Fremont Peak. The dolomite bands stand out in 
 relief from the limestone matrix. 
 
 any rock so mapped could be used in manufacture of 
 portland cement without extensive beneficiation or with- 
 out prohibitively expensive selective mining. However, 
 within this unit are small patches of good limestone and 
 others of good dolomite which could be quarried selec- 
 tively for an operation that does not require large ton- 
 nages or utilize massive mining procedures. 
 
 Siliceous Limestone with Minor Dolomite (ds). The 
 unit mapped as siliceous limestone with minor dolomite 
 includes various proportions of limestone and dolomite 
 plus replacement patches of silica in the form of quartz- 
 ite, and scattered veins and replacements of barite. The 
 rock is virtually unusable for any commercial purpose 
 except aggregate and fill unless it is crushed and the 
 principal mineral constituents calcite, dolomite, quartz i 
 and, locally, barite, are separated. 
 
 Limy Siliceous Dolomite (dosl). The unit mapped 
 as limy siliceous dolomite is chiefly blue-gray, medium- 
 grained calcitic dolomite containing considerable quartz 
 and miscellaneous silicate minerals formed by contact 
 
 I # 
 
 1". Detail of banded carbonate rocks on the south slope of Fremont Peak showing the cup-shaped solution pits that 
 develop on limestone and the seamed surface of relief on the dolomite bands. The outcrop is about six feet wide. 
 
1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 19 
 
 +*'- 
 
 w* 
 
 % v 
 
 
 . 
 
 
 Photo 18. A landscape just east of the Fremont Peak park headquarters. The rounded hill is underlain by gray, 
 vuggy quartzite formed by replacement of dolomitic limestone. Patches of gray replacement silica of this sort are found in 
 several places in the Fremont Peak district, but this mass, covering more than seven acres, is the largest. 
 
 metaraorphism. These rocks stand out boldly on weath- 
 ered surfaces, particularly where they are in contact 
 with limestone. Most samples analyzed contain more than 
 15 percent MgO and 9 percent Si0 2 . Possible commercial 
 usage would depend entirely upon the cost of separation 
 of calcite, dolomite, quartz, and silicate mineral grains, 
 and upon the percentage of waste residue. 
 
 Gray Quartz (q): The material mapped as gray 
 quartz is light gray, commonly vuggy quartz rock formed 
 by replacement of carbonate rock. The large mass which 
 extends east from Fremont Peak State Park boundary 
 onto Reeves Ranch might be usable as a source of silica. 
 It contains several hundred thousand tons of uniform 
 material, but no analyses are available. 
 
 Limestone with Granitic Rock and Schist Intercala- 
 tions (Isqs) : This unit consists of limestone and dolo- 
 mite interleaved with quartz-mica schist, quartz monzo- 
 nite and other granitic rocks. The proportion of car- 
 bonate rock to granitic rock is commonly small. Schist 
 and granitic rock are commonly present in roughly equal 
 proportions. 
 
 Quartz-Mica Schist (sch): The quartz-mica schist 
 unit consists of quartz-biotite-muscovite schist, commonly 
 containing a little feldspar and locally containing anda- 
 lusite, sillimanite, tremolite, and wollastonite, singly or 
 together; it is probably derived from clay shale. 
 
 Pink Quartzite (qp): The pink quartzite is a well- 
 bedded, slightly micaceous quartzite probably derived 
 from sandstone. Pinkish to vitreous hues prevail on fresh 
 surfaces. Weathered surfaces commonly are rusty brown. 
 It is generally associated with schist. 
 
 Schist and Granitic Rock (grs) : This unit contains 
 intimately mixed quartz-mica schist, pink quartzite, and 
 gneissoid to schistose quartz monzonite. It is commonly 
 cut by pegmatite and aplite dikes. 
 
 Granitic Rocks (gr) : The granitic rocks are largely 
 biotite quartz monzonite with local intrusions of biotite 
 granodiorite. 
 
 SEQUENCE AND STRUCTURE IN THE 
 FREMONT PEAK ROCKS 
 
 Sur Series Section 
 
 The Sur series section at Fremont Peak was selected 
 for study because it seemed the thickest, most nearly 
 intact sequence in the northern Gabilan Range. Detailed 
 mapping, however, revealed that the section was dis- 
 rupted in several places by granitic rocks which shoul- 
 dered aside the invaded metasediments, and that nowhere 
 could tops and bottoms of beds be determined with 
 certainty because of the amount of deformation and 
 degree of metamorphism to which the rocks had been 
 subjected. Inasmuch as overturning in any part of the 
 section cannot be proven or even suggested, and inas- 
 much a.s the layered rocks dip uniformly north at steep 
 angles in the neighborhood of 70 degrees, it may be 
 assumed that the older or lower part of the section lies 
 south of Fremont Peak and that the younger or upper 
 beds of the sequence lie to the north in a homoclinal suc- 
 cession. If these assumptions are accepted, the Sur series 
 sequence top to bottom (see section AA on the map) can 
 be described as follows : 
 
20 
 
 CALIFORNIA DIVISION OP MINES 
 Sur series section at Fremont Peak. 
 
 [Special Report 56 
 
 Stratigraphic unit 
 
 Lithology 
 
 Thickness in feet 
 
 Subunit 
 
 Unit 
 
 Upper schist- 
 
 Middle carbonate schist - 
 
 Subunit 1 - 
 
 Subunit 2 
 
 Subunit 3 
 
 Subunit 4__ 
 
 Subunit 5 . . 
 
 Subunit 6 
 
 Subunit 7 
 
 Subunit 8 
 
 Subunit 9 
 
 Subunit 10 
 
 Subunit 11_. 
 
 Subunit 12 
 
 Subunit 13 
 
 Subunit 14__ 
 
 Lower schist . 
 
 Subunit 1 
 
 Subunit 2 
 
 Subunit 3 
 
 Brown quartz-mica schist with some interleaves of quartz monzonite. 
 
 White, coarse-crystalline limestone 
 
 Bluish medium-crystalline limestone 
 
 Black amphibolite 
 
 Brown quartz-mica schist 
 
 Gray limestone with cream-colored dolomite 
 
 Brown schist interbedded with pink quartzite 
 
 Gray limestone with cream-colored dolomite 
 
 Brown quartz-mica schist with quartzite 
 
 Gray limestone; no dolomite.. . 
 
 Gray limestone with cream-colored dolomite 
 
 Brown quartz-mica schist with interleaved quartzite and quartz monzonite 
 
 Cream-colored dolomite with relict patches of gray limestone 
 
 Gray limestone; no dolomite 
 
 Brown quartz-mica schist; limestone lenses 
 
 Brown quartz-mica schist 
 
 Gray limestone with cream-colored dolomite 
 
 Brown quartz-mica schist with interleaved quartz monzonite. 
 
 100 
 170 
 100 
 60 
 335 
 160 
 375 
 165 
 125 
 290 
 500 
 400 
 360 
 280 
 
 1,100 
 
 160 
 
 2,250 
 
 1,415 
 3,420 
 
 3,510 
 
 Total 8,345 
 
 J* 6 
 
 Mrs*; % frl> 
 
 ; r ( 
 
 ,*• "■% 
 
 *>i 
 
 ■ • - 
 
 
 * 
 
 \ H 
 
 • r V\\ 
 
 ml 
 
 
 
 Y 
 
 %£m^ 
 
 
 
 Jb 
 
 
 WW 
 
 "^ 
 
 
 « - 
 
 
 i 
 
 
 .^•' 
 
 •^t.. 
 
 V 
 
 a:#k 
 
 L . 
 
 - ^ 
 
 Hackly, lichen-covered surfaces of replacement quartz cropping out a quarter of a mile east of Fremont Peak 
 
 park headquarters. 
 
1959] LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 21 
 
 For comparative purposes the section across a large seated succession. (See accompanying cross section.) In 
 
 Sur series pendant west of Gabilan School is reproduced the present state of erosion the granitic rocks which have 
 
 from Allen (1946, p. 20) as follows: welled up under the Sur series have been exposed and 
 
 Fine-grained mica schist 200 ft. themselves deeply eroded. Many of the carbonate-rock 
 
 Limestone _. 250 ft. deposits cannot, therefore, be expected to carry down- 
 Limestone ~ I 300 ft ward more than a few hundreds of feet, whereas prior 
 
 Quartzite, pure, well-bedded 180 ft. to erosion they carried down many thousands of feet. 
 
 — The shallow nature of the carbonate-rock pendants crop- 
 Total _ 980 ft. pj ng out a i on g. Rocky Ridge west of Fremont Peak is 
 
 It is the belief of the authors that the thickness of wel1 shown in the lower tunnel of the ba.rite workings 
 units mapped as "schist and quartz monzonite" have not where the thickness of carbonate-rock has lessened ma- 
 been appreciably increased through invasion of granitic terially from what it is at ridge crest, 
 material, at least along the chosen line of cross section. Rocky Ridge Fault Zone 
 Much of the granitic rock within these units is schistose . . 
 
 or gneissoid and abnormally high in quartz and micas, A nar r °Z f ™ of brecciation follows the north slope 
 
 indicating that it has formed mainly by transformation of Rocky Ridge for more than a mile beginning at the 
 
 of aluminous sediment such as clay shale. The proba- road U P the eJ \ st face ° £ P "P° nt Peak - J h f bant f mm " 
 
 bility of thinning of the units by "compression during eralization and sporadic sihcification of the carbonate 
 
 folding is much greater than the probability of material roek follows \ his zo " e i; of brecciation. The zone apparently 
 
 thickening of any of the units through addition of gra- represents a line of faulting older than the invasion of 
 
 nitic material. Some of the carbonate units undoubtedly the granitic rock Granitic rock and schist probably have 
 
 have been thickened at some points and thinned at others J 10 * been involved in the brecciation, although accumu- 
 
 bv plastic flow during folding. latl0ns , °J talus m f k * he z ° ne n ! s « veral P la f s - The 
 
 * The following conclusions may be drawn from a study several short, northeast-trending faults mapped at the 
 
 of the stratigraphic succession in the Fremont Peak area: cre f ° f . Rock ^ R^ge probably are related to this line 
 
 1. The limestone and dolomite are not confined to any °! 1 fa ? t ^! s - The ma « nltude + of movement along this prob- 
 particular horizon or horizons in the Sur series sequence ; able ^ult cannot be ascertained as no significantly dif- 
 
 f, ,, -, n A + +• x,- ™„„i,. iLj„ „„ terent units have been brought into contact and the 
 
 there are no well-defined stratigraphic marker beds or . . , ^ .. 
 
 v • i • ,i topojjrap nc expression is not distinctive, 
 
 horizons anywhere m the sequence. F " ' F 
 
 2. The dolomite is present as replacement patches of „,„.,,„_„ ,,„_,.,., ,„, _„,.,.. AT , K .^ TL ,^ 
 
 i •* -i.u- i v 4. i FIELD FEATURES USEFUL IN ESTIMATING THE 
 
 extreme irregularity within larger limestone masses and -*^„«....«. „^„„.„.. .,-..-„ ^- ,...- 
 
 , -x • t !.• £ *■ i • ECONOMIC POSSIBILITIES OF THE 
 
 nowhere is its presence indicative of any particular posi- „.„„«.,„„ „„„„ ..»„„.-„ 
 
 .. . ,, \. , . * ^ v CARBONATE-ROCK MASSES 
 tion in the stratigraphic sequence. 
 
 3. Because of the extreme irregularity of distribution In the climate that prevails over the Gabilan Range 
 of dolomite in the carbonate-rock masses, presence of the carbonate rocks weather and erode far less readily 
 magnesium, the chief element controlling the commercial than the enclosing schist and granitic rocks. Hence they 
 utilization of the carbonate rocks, must be carefully stand out boldly in relief and may give a false impres- 
 checked by adequate sampling and chemical analysis of sion in estimating reserves. In areas where schist inter- 
 file samples. beds and granitic rocks may be numerous, accumulations 
 
 4. Most of the potentially commercial limestone and of talus and soil mantle may mask them. Presence of 
 dolomite deposits in the northern Gabilan Range are in granitic rock and schist in an apparently homogeneous 
 the central 3,000- to 4,000-foot thickness of the Sur mass of carbonate rock may generally be detected by 
 series, and are likely to be found enveloped in several presence of granitic and schist debris in the soil and by 
 thousand feet of mica schist. '& the distribution of erosion depressions worn into the 
 
 The metasedimentary rock units of 'the Fremont Peak softer rocks, 
 
 section appear to be "in conformable succession; and, As previously mentioned, limestone and dolomite in 
 
 although neither the top nor base of the series can be the Fremont Peak vicinity may be differentiated on 
 
 observed because of obliteration by granitic intrusions, weathered surfaces with considerable accuracy by dif- 
 
 the 8345 feet of beds present in the Fremont Peak section ferences in grain relief, grain size, and color. Limestones 
 
 probably represents only part of the original thickness of the Fremont Peak area are almost invariably coarser 
 
 of the sequence. As can'be seen from the accompanying grained and less dense than the replacing dolomite. On 
 
 map all three of the crudely defined units of the Sur se- weathered surfaces of mixed carbonate rock, dolomite 
 
 ries include both carbonate-rock and schist subunits. It is stands out in relief from matrix calcite because of its 
 
 also apparent that many of the subunits are lenticular greater resistance to weathering. So also do quartz and 
 
 and non-persistent, even in the small area mapped, and other silicate minerals, but these are detected by large 
 
 that the original succession was heterogenous. In addi- differences in hardness and texture between them and 
 
 tion the strong compressive deformation the metamor- the carbonate minerals. Dolomite most commonly weath- 
 
 phic rocks have been subjected to has undoubtedly caused ers pale buff or cream because of the slightly increased 
 
 thickening and thinning of many of the members, par- iron content of most dolomites. Limestones range from 
 
 tieularlv by means of plastic flow in the carbonate units. pure white through light gray to dark gray, or variega- 
 
 There are a number of structural features unrelated tions of these colors, and rarely weather buff or cream. 
 
 to the stratigraphic succession that should be mentioned. Pure white, medium-grained, crystalline dolomites were 
 
 The homoelfnal metasediments at Fremont Peak repre- observed only at the Natividad and Bird Creek Cienega 
 
 sent only the roots of a formerly vast, much deeper- districts. Coarse-grained dolomites were not observed. 
 

 CALIFORNIA DIVISION OF MINES 
 
 [Special Report 56 
 
1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 23 
 
 Solution pits in dolomite generally are fewer and less 
 complex than those seen on weathered limestone surfaces 
 and they commonly develop in crisscrossing linear pat- 
 terns controlled by joints. Limestone surfaces are gener- 
 ally more universally and deeply pitted than dolomite 
 surfaces and lack the linear pit patterns. Unfortunately, 
 most of the readily apparent differences mentioned above 
 do not apply to freshly broken surfaces, so that they are 
 of little value to the quarryman. Chemical analysis or 
 staining with chemicals such as ferric chloride or cupric 
 nitrate are the most suitable methods of estimating cal- 
 cite-dolomite proportions in drill cores or freshly quar- 
 ried samples. 
 
 Where quartz or silicate minerals have been intro- 
 duced into the carbonate rocks by contact metamorphism 
 or have developed during metamorphism from original 
 impurities, they generally stand out in relief on weath- 
 ered surfaces of either limestone or dolomite. Conse- 
 quently, rocks having: prohibitively large proportions of 
 such minerals are easily detected on weathered surfaces. 
 Silicate-mineral impurities generally are also visible on 
 freshly broken surfaces of carbonate rocks because of 
 hardness and color differences. 
 
 An additional feature, probably applicable only to the 
 rocks of the Gabilan Peak vicinity, is that carbonate 
 rocks containing more than 2 or 3 percent silica generally 
 contain too great a proportion of magnesium to be use- 
 able in portland cement. As the siliceous minerals nor- 
 mally are detectable on weathered surfaces and com- 
 monly on broken surfaces too, their presence may be 
 used as a field guide in prospecting for cement rock. 
 
 ECONOMIC POSSIBILITIES OF LIMESTONE AND 
 DOLOMITE DEPOSITS 
 
 The following section of the report deals with most of 
 the deposits in the Gabilan Range north of the latitude 
 passing through Chualar which are sufficiently extensive 
 and reasonably accessible to be of economic interest. It 
 is arranged geographically north to south by districts 
 and alphabetically by deposit within each district. Be- 
 cause of time limitations, it has not been possible to 
 examine or describe each deposit in detail, and the fol- 
 lowing data are intended to indicate the general eco- 
 nomic possibilities of the deposits rather than to describe 
 them in detail. 
 
 Los Vergeles District (1) * 
 
 The geologic map of San Juan Bautista quadrangle 
 (Allen, 1946) shows a gently curving arc of limestone 
 pendants extending northwest across the San Juan Grade 
 (the county road connecting San Juan Bautista and 
 Salinas) between Mud Creek and Crazy Horse Canyons. 
 Most of the pendants are on Los Vergeles Ranch. One 
 of these pendants is well exposed in a small roadside 
 quarry on the west side of the road 3 miles northeast 
 of Lagunita reservoir. It is also well exposed on grazing 
 land east and west of the San Juan Grade. 
 
 The crystalline limestone is blue-gray to white on 
 fresh surfaces and generally weathers to a light blue- 
 gray. Rock textures range from medium coarse-grained 
 (cleavage surfaces averaging about 5 mm in longest 
 dimension) to fine-grained (grains averaging less than 
 
 * Numbers following the name of deposit or district correspond with 
 map locations on figure 4. 
 
 1 mm in longest dimension). Analyses of the rock are 
 not available, but a small tonnage, apparently taken from 
 the San Juan Grade quarry sometime during the period 
 1906-25 was found suitable for steel flux (Laizure, 1925, 
 p. 43). Much of the rock exposed in fields east of the 
 San Juan Grade shows replacement patches of silica and 
 dolomite. Exposures to the northeast of the Crazy Horse 
 Canyon road show even more extensive contamination 
 by masses of dolomite and silica. Any deposit developed 
 for commercial usages other than aggregate would have 
 to be carefully sampled and tested. In most places, the 
 selective mining that would be necessary to maintain 
 a uniform grade of rock probably would prove prohibi- 
 tively expensive. The largest lenses lie toward the 
 northern end of the arcuate belt of pendants adjacent 
 to Crazy Horse Canyon. 
 
 San Juan Canyon District 
 
 The San Juan Canyon district lies astride San Juan 
 Canyon 3 to 5 miles southeast of San Juan Bautista. 
 Deposits are nearly all limestone, no potentially com- 
 mercial dolomite deposits having been found in the vi- 
 cinity. The Ideal Cement Company plant at San Juan 
 Bautista is supplied from deposits of this district. Al- 
 though the deposits are not particularly large, the mag- 
 nesium problem, ever present in other districts, is not 
 critical in the San Juan Canyon district. 
 
 Barbee Ranch Deposits (2) 
 
 The Barbee Ranch deposits consist of several concen- 
 trations of fragmental carbonate rock astride Barbee 
 Canvon 1 mile south of the Ideal cement plant in the 
 N| SEi sec. 9, T. 13 S., R. 4 E., M.D. The mineral rights 
 are held by Ideal Cement Company. Some rock has been 
 taken from the vicinity in past years, probably for trial 
 purposes, but nothing has been taken in recent years. 
 Reserves are believed to be small. Blocks and boulders 
 of crystalline limestone mixed with soil and non-car- 
 bonate talus crop out in a. narrow belt crossing Barbee 
 Canyon in a southeasterly direction. According to Allen 's 
 map (1946) this material is part of the steep-dipping 
 lower Miocene Vaqueros formation. Typical samples col- 
 lected and analyzed by the cement company yielded the 
 following results : 
 
 CaO MgO AUO, Fe,0, K t O Na,0 SiOi 
 
 Sample 1 54.86 .4.'? 1.26 .40 NT).* N.I). 1.46 
 
 Sample 2 54.86 .52 .8!) .33 N.D. N.I). 1.06 
 
 Sample 3 51.02 .57 1.73 .75 .06 .07 5.10 
 
 * Not determined. 
 
 Bryan and Pearce-Twohy Deposits (3) 
 
 The Bryan and Pearce-Twohv properties lie in the 
 N^ sec. 24 (projected), T. 13 S., R. 4 E., and in the WJ 
 sec. 19 (projected), T. 13 S., R. 5 E., M.D., in what was 
 originally part of the Spanish grant Cienega del Gab- 
 ilan. They adjoin and cover elements of the same lime- 
 stone mass. Both properties are leased by Ideal Cement 
 Company; they constitute the principal current source 
 of supply for the San Juan Bautista cement plant. 
 
 The limestone mass is an elongate lens set on edge 
 between granite and quartz-mica schist walls. The mass 
 is slightly arcuate in plan, irregular in outline, and 
 oriented with its longest direction trending northwest. 
 It reaches a maximum width of 400 feet, an exposed 
 depth of 700 feet, and has been traced along its length 
 
24 
 
 CALIFORNIA DIVISION OF MINES 
 
 [Special Report 56 J 
 
 
 Wt 
 
 *40 
 
 » 
 
 ■ ■ ■*..- 
 
 Photo 20. Ideal Cement Company plant near San Juan Bautista, observer facing south. The plant utilizes 
 crystalline limestone and weathered granite and schist obtained locally, and clay shale hauled in from Chittenden 
 at the south end of Santa Clara Valley. 
 
 PHOTO 21. Underwood and Pearce-Twohy quarries of Ideal Cement Company three miles south of San Juan 
 ista as seen from the Fremont Peak road, observer facing northeast. The quarries are in white crystalline 
 one pendants, The pendants are enveloped in granitic rocks and schist and some granitic dike rocks penetrate 
 the limestone masses. 
 
1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GAB1LAN RANGE 
 
 25 
 
 for about 3,000 feet. Indicated reserves are roughly 20,- 
 000,000 tons, but part of this tonnage is not readily 
 recoverable because of unfavorable stripping ratios or 
 necessity for underground mining. 
 
 The average analysis obtained by taking the mean of 
 50 typical surface samples and 500 feet of diamond 
 drill cores (samples analyzed by the Ideal Cement Com- 
 pany laboratory) is as follows: 
 
 CaO 51.1 
 
 MgO 1.4 
 
 C0 2 41.7 
 
 Si0 2 4.1 
 
 Fe 2 3 ) 
 AU0 3 J 
 
 1.7 
 
 Flint-Steinbeck Deposit (4) 
 
 This deposit is If airline miles west and slightly south 
 of the Pearce-Twohy deposit. The quarries are in sec. 
 23, T. 13 S., R. 4 E, M.D. and were driven into both 
 sides of the ridge that forms the southeast wall of Stein- 
 beck (Steinbach) Canyon. It was once a major source 
 of supply for the cement plant at San Juan Bautista, 
 but has been idle for many years. 
 
 Limestone occurs in a lono- thin lens, set on edge, 
 the edge trending N. 80° E. The sheetlike mass, tapered 
 at both ends, dips steeply south, has a traceable length 
 of nearly 3,000 feet and an average width of about 100 
 feet. It has been exposed to a maximum depth of 440 
 feet by erosion but probably continues below the level 
 of the adjacent canyon-bottoms. Wall rocks are granite 
 and quartz-mica schist. The limestone is similar in phys- 
 ical character and chemical content to the rock from 
 the Bryan and Pearce-Twohy properties. Considerable 
 limestone remains in the lens but recovery would be 
 expensive because of the attitude of the mass and be- 
 cause of the steepness of the topography. Much of the 
 remaining material would have to be mined underground 
 or else stripped at high cost. 
 
 Harmony Hills Deposit (5) 
 
 The Harmony Hills deposit is located at the north 
 end of the Crowe-Harris ranch close to the Fremont 
 Peak State Park road on part of the Cienega del Gabilan 
 land grant. It is near the center of sec. 20 (projected), 
 T. 13 S., R. 5 E., M.D. A dirt road crossing the deposit 
 connects with the Fremont Peak road. 
 
 White, coarsely crystalline limestone occurs in an 
 east-trending lenticular mass the exact outlines of which 
 are masked by soil and undergrowth. The mass is at 
 least 750 feet long and the thickest part of the lens 
 reaches 150 feet. Erosion has exposed the rock to a depth 
 of 60 to 80 feet. Probably reserves are well in excess 
 of 1,000,000 tons. A typical clean surface sample col- 
 lected by the authors yielded the following analysis 
 (Abbot A. Hanks, San Francisco, analysts) : 
 
 CaO H2.37 
 
 Mgo 2.eo 
 
 SiU 2 -32 
 
 Fe 2 O a -08 
 
 AU0 3 - 14 
 
 p s o s 01 
 
 Remainder 44.48 (chiefly CO s ) 
 
 Underwood Deposits (6) 
 
 The Underwood deposits are a series of small, discon- 
 tinuous masses of limestone located near the San An- 
 dreas fault zone close to and on the northeast side of 
 
 the San Juan Canyon Road half a mile north of the 
 Pearce-Twohy deposit. The Underwood property is part 
 of the former Cienega del Gabilan land grant. It was 
 operated for many years as a source of cement rock by 
 the San Juan Portland Cement Company. The limestone 
 reserves have been largely depleted and the quarries 
 have been long idle. 
 
 The limestone masses arc within a triangular area 
 bordered on the north and east by faults and on the 
 west by San Juan Valley alluvium. The total reserves 
 probably never exceeded a million tons, and individual 
 masses ranged from a few thousand tons to several hun- 
 dred thousand tons. The masses are in granite and 
 quartz-mica schist wall rocks. The rock is similar in 
 character to that of the Bryan and Pearce-Twohy de- 
 posits. 
 
 Natividad District 
 
 The Natividad district includes those deposits within 
 the angle formed by the course of Gabilan Creek where 
 it turns southwest to debouch into Salinas Valley. Most 
 of the deposits lie between the town of Natividad, on 
 the south, and Sugarloaf Peak on the north. Dolomite 
 deposits greatly predominate over limestone deposits and 
 nearly all of the commercial production from the dis- 
 trict has been from dolomite pendants. The commercial 
 dolomite rock is snow white and medium crystalline, and 
 in chemical composition is near that of the pure mineral 
 dolomite. The best deposits lie south of Sugarloaf Peak, 
 as those of Sugarloaf Peak have been extensively con- 
 taminated by iron oxides. Elsewhere, the iron content 
 seldom exceeds 0.2 percent. 
 
 Kaiser Aluminum and Chemical Company Deposits (7) 
 
 Kaiser Aluminum and Chemical Company controls 
 most of the commercially desirable pendants of dolomite 
 near Natividad. These deposits supply two plants, one 
 at Natividad and one at Moss Landing. Opened in 1943, 
 the various quarries have furnished close to 3,000,000 
 tons of dolomite over the 14-year period. 
 
 Most of the dolomite has been quarried from a single 
 irregular mass aggregating almost three-quarters of a 
 square mile in plan. According to Allen (1946, p. 69), 
 the dolomite strikes N. 60-70° W. and dips 40-45° NE 
 but bedding is hard to identify in any of the quarry 
 faces. The mass has been exposed by erosion and quarry- 
 ing through a depth of 700 feet, but the lower surface 
 is very irregular and numerous dikes and sills of granitic 
 rock hinder quarrying and processing of the dolomite. 
 Waste material from the quarrying process sometimes 
 reaches 50 percent (Logan, 1947, p. 257). The rock is 
 uniform, snow-white, medium-crystalline material, the 
 roughly circular cleavage surfaces averaging 2 to 3 mm 
 in diameter. Virtually the only contaminating materials 
 come from granite intrusions and from stains coating the 
 joint surfaces. Because of the numerous altered granitic 
 intrusions and resultant poor recovery of diamond drill 
 cores, estimation of reserves is crude ; but the main mass 
 may contain as much as 100 million tons of dolomite of 
 relatively uniform commercial grade. A representative 
 analysis, furnished by the company is as follows : 
 
 CaO 31.7 
 
 MrO 20.5 
 
 SiOi 1.0 
 
 Fe 2 Oa 0.2 
 
 AUOa 0.2 
 
 C0 2 40.4 
 
26 
 
 CALIFORNIA DIVISION OF MINES 
 
 [Special Report 56 
 
1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 27 
 
 Photo 23. Quarries and waste dumps at the Xatividad plant of Kaiser Aluminum and Chemical Corporation. Granitic 
 intrusions into the dolomite cause a high proportion of waste, but the white crystalline dolomite is of unusually high purity 
 and total reserves are estimated to be about 100 million tons. 
 
 
 -^*£0' 
 
 
 Photo 24. A quarry face and i 
 
 oor at the Xatividad operation of Kaiser Aluminum and Chemical Corporation. 
 
28 
 
 CALIFORNIA DIVISION OF MINES 
 
 [Special Report 56 
 
 
 
 
 
 
 
 
 *?S 
 
 
 
 , *? 
 
 4b * '"^6BJS- 
 
 *^^ 
 
 
 
 
 
 
 
 
 
 
 * w 
 
 * 
 
 '-•• •,,.-* 
 
 
 
 f?*&Fi 
 
 *" 
 
 
 
 . *- 
 
 s 
 
 Hs 
 
 
 
 ■:.'4"-. 
 
 MgO 
 
 S 
 
 P 
 
 Mn 
 
 R 0:> 
 
 CO? & HoO 
 
 11.20 
 
 .004 
 
 .010 
 
 .06 
 
 .52 
 
 45.64 
 
 20.67 
 
 .003 
 
 .008 
 
 .05 
 
 .90 
 
 45.10 
 
 20.35 
 
 .003 
 
 .006 
 
 .05 
 
 .50 
 
 46.53 
 
 Photo 25. A newly blasted "boulder" of dolomite on the floor 
 of one of the Natividad quarries showing dikelets of granite peg- 
 matite cutting the dolomite. Granitic intrusions are the principal 
 detriment to quarry practice in this vicinity. 
 
 Porter Dolomite Deposit (7a) 
 
 Owned by James Porter, 701 Old Stage Road, Salinas, 
 California. Located 1£ miles south of the Kaiser holdings 
 and 1£ miles east of Natividad. The deposit is roughly 
 300 feet wide and 3,000 feet long, with an east elonga- 
 tion and nearly vertical dip. Granitic intrusions pene- 
 trate the mass in many places. Most of the rock is white, 
 medium crystalline dolomite similar to that in the Kaiser 
 deposits. Three adjacent 10-foot-long chip channel 
 samples cut perpendicular to the strike probably reflect 
 the chemistry of the deposit. Much of the deposit cor- 
 responds to samples 2 and 3. 
 
 Sample Fe SiOj AliO;i CaO 
 
 1 .10 1.52 .38 41.20 
 
 2 .40 .68 .30 33.00 
 
 3 .20 .84 .21 32.00 
 
 Sugar-loaf Deposits (8) 
 
 A broad belt of carbonate rock 600 to 700 feet 
 wide and over a mile long crosses Sugarloaf Peak in a 
 northeasterly direction. The southwest third of the mass 
 is mainly dolomite but toward the northeast this grades 
 into mixed dolomite-calcite rock. Northeast of the crest 
 the mass is poorly exposed because of thick brush and 
 soil mantle. Thus far, there has been no commercial 
 utilization of the Sugarloaf Peak rocks. 
 
 The dolomite is grayish-white, mottled with small 
 spots and clots of red iron oxide. Veinlets of iron oxide 
 and ferruginous silica cut the mass in numerous places. 
 Where the carbonate mass is poorly exposed east of the 
 peak, float consists of medium-grained and coarse- 
 grained blue-gray to white dolomitic limestone and 
 finer-grained off-white dolomite. 
 
 Because of the impure nature of the dolomite on the 
 southwest slope of Sugarloaf Peak and because of the 
 apparent mixture of calcite and dolomite rock east of the 
 peak, it is doubtful if satisfactory commercial deposits 
 can be developed in this vicinity. 
 
 Other Deposits 
 
 Several large pendants were mapped by Allen (1946) 
 east and northeast of Natividad, but he does not describe 
 them in the text and does not differentiate the limestone 
 
 and dolomite masses. Bethlehem Steel Company (for- 
 merly Pacific Coast Steel Co.) produced dolomite from a 
 small quarry half a mile north of the Kaiser Aluminum 
 and Chemical Company Quarries at various times between 
 1900 and 1940. Allen (1946, p. 67) mentions production 
 of limestone from the district about 1900 for use in 
 beet-sugar manufacturing, but the quarry is misidenti- 
 fied. The authors had no opportunity to examine deposits 
 other than those of Kaiser Aluminum and Chemical 
 Company and Sugarloaf Peak, but it is probable 
 that most of the others consist of mixed masses of cal- 
 cite and dolomite rock and that there are no other sub- 
 stantial deposits of commercial dolomite or limestone in 
 the district. 
 
 Fremont Peak District 
 
 As previously described, the Fremont Peak district 
 includes vast pendants of carbonate rock, but most of 
 these consist of intermingled masses of calcite and dolo- 
 mite rock that are not of present commercial interest. 
 Also, the remoteness of the district from utilities and 
 from rail and truck transportation reduces the chances 
 for exploitation of the deposits in the near future. Most 
 of the deposits lie on the Reeves and Bardin ranches, 
 parts of the Spanish grant Cienega del Gabilan. They 
 lie in an east-trending belt along the slopes of Rocky 
 Ridge and Fremont Peak, the belt dying out toward the 
 east in the Bird Creek drainage basin. None of the de- 
 posits in this district has been utilized commercially 
 thus far. 
 
 Bardin Ranch Deposits on Rocky Ridge (9) 
 
 Three small patches of limestone of potential com- 
 mercial grade are outlined on the geologic map which 
 accompanies this report, on the south slope of Rocky 
 Ridge about 1 mile west of Fremont Peak. Part of the 
 rock in these deposits is medium-grained, blue-gray 
 material suitable for general use where color is not im- 
 portant, and part is coarse-grained, pure-white material 
 suitable for whiting and white filler. None of the de- 
 posits has been developed or tested except for a few 
 samples taken by the authors but, judging from surface 
 exposures, more than a million tons of commercial ma- 
 terial might reasonably be developed in the three masses. 
 They are currently accessible by Gabilan Creek Canyon 
 via unimproved dirt road. 
 
 East Gabilan Deposit (10) 
 
 The East Gabilan deposit is the largest in the Fre- 
 mont Peak district and is situated on terrain favorable 
 to low-cost quarrying. It is on the Reeves Ranch just 
 west of the main ranch access road three-quarters of a 
 mile east and slightly south of Fremont Peak. The areal 
 extent is shown on the accompanying geologic map. The 
 mineral rights for this part of the Reeves Ranch are held 
 by Ideal Cement Company. 
 
 As seen in plan, the limestone mass averages about 300 
 feet in width and is approximately 2,800 feet long. The 
 beds, though crudely defined, strike N. 70-80° W. and 
 dip 65-80° N. Erosion has exposed limestone to a depth 
 of 140 feet below the highest outcrops and the mass has 
 been penetrated by several hundred feet of adits driven 
 for sampling purposes by predecessors to Ideal Cement 
 Company. Although overlain stratigraphically by dolo- 
 mite and dolomitic limestone, the stratigraphic sequence 
 
1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN CiABILAN RANGE 
 
 29 
 
 Photo 26. A typical landscape on the Reeves Road west of Vineyard School showing initial stages in exploration of a 
 dolomite deposit by Westvaco Chemical Division of Food Machinery and Chemical Corporation. The brush-covered deposit 
 has been laid bare by a bulldozer cut and a diamond-drill rig is working. 
 
 
 'ir-v^ — 
 
 A closer view of the diamond drill rig shown in photo 2G. 
 

 • : *»''<£ 
 
 
 
 
 \; - 
 
 * >iSw v 
 
 \~ s -J**^-- 
 
 ■<4b^-.-jC*.s, 
 
 r 
 
 J 21" ; 
 
 -^ LIT* 1 - 
 
 •' L 
 
 
 ^•v**- 
 
1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 31 
 
 Photo 28. (opposite). Bouldery limestone outcrops on oak 
 savannah at the power line deposits on the Reeves Ranch. These 
 deposits are among the largest undeveloped reserves in the Cienege- 
 Vineyard district. 
 
 dips too steeply for such material to cause an overburden 
 problem. Over most of the deposit there is no overburden 
 whatever. Estimated reserves calculated to a depth of 
 240 feet below the uppermost outcrops (a reasonable 
 recovery depth) total approximately 16,000,000 tons. 
 Substantial additional tonnage could be developed by 
 underground mining methods. The following analyses are 
 typical of the limestone. Samples 1-3 were done by Ideal 
 Cement Co. ; samples 5-7 by Abbot A. Hanks Inc. 
 
 Oxide #1 #2 #3 #4 #5 #6 #7 
 
 CaO 55.42 54.42 54.73 54.43 54.37 54.35 54.02 
 
 MgO .41 .92 .41 .53 .45 .48 .99 
 
 Si0 2 .24 .94 1.52 .86 .86 .92 .82 
 
 Fe,Oa .20 .14 .32 .11 .08 .11 .13 
 
 AbOa .10 .14 .34 .29 .26 .17 .13 
 
 K 2 .03 .02 .06 N.D. N.D. N.D. N.D. 
 
 Na»0 .04 .03 .02 N.D. N.D. N.D. N.D. 
 
 P,0 6 N.D.* N.D. N.D. .06 .03 .02 .02 
 
 Ignition loss ___ 43.72 43.53 43.18 43.72 43.95 43.95 43.89 
 (chiefly C0 2 ) 
 * Not determined. 
 
 Fremont Peak Deposits (11) 
 
 Four substantial masses of limestone of probable com- 
 mercial grade are grouped together about a quarter of 
 a mile southeast of Fremont Peak. These appear on the 
 accompanying geologic map. The authors are not fa- 
 miliar with property boundaries in the vicinity, but the 
 limestone masses appear to be partly on the Bardin 
 Ranch and partly on Reeves'- ranch. Probable reserves 
 aggregate a million tons. The rock typically is light 
 blue-gray and ranges from medium to coarse crystalline. 
 The following analyses are representative of the rock. 
 Analyses are by L. A. Caetano, courtesy of Ideal Cement 
 Company. 
 
 Oxide Sample G-13 
 
 Sample G-14 
 
 Sample G-15 
 
 CaO 55.02 
 
 53.94 
 
 55.52 
 
 MgO .69 
 
 1.53 
 
 .46 
 
 SiOs 1.58 
 
 .42 
 
 .14 
 
 ALO3 .58 
 
 .08 
 
 .17 
 
 Fe^Oa .30 
 
 .08 
 
 .13 
 
 K2O .03 
 
 .01 
 .01 
 
 .01 
 
 Na a O .04 
 
 .04 
 
 Ignition loss 42.14 
 
 43.62 
 
 43.60 
 
 (chiefly C0 2 ) 
 
 
 
 Bird Creek District 
 
 Included in this district are the deposits found on 
 the slopes of the Bird Creek drainage system. The dis- 
 trict adjoins the Fremont Peak district on the east, there 
 being no well-defined gap between them. Most of the 
 carbonate-rock pendants are limestone, and commercial 
 dolomite deposits have not thus far been found in the 
 district. The terrain is rugged and the vegetation is so 
 dense that not all of the carbonate-rock masses have 
 been explored. None of the deposits have been commer- 
 cially exploited thus far although several of them are 
 being held for future commercial use. The district falls 
 entirely within the boundaries of the Crowe-Harris, 
 Reeves, and Martin ranches. 
 
 A.S. and R. Deposit (12) 
 
 The American Smelting and Refining Company held 
 tin 1 A. S. and R. deposit for many years and at one 
 time planned to build rail connections to it. The deposit 
 is on the Crowe-Harris ranch at the confluence of Bird 
 Creek and North Canyons. Pure white, and blue-gray 
 and white variegated, coarsely crystalline limestone is 
 in a thin, lenticular, vertical-standing pendant within 
 granite and schist walls. It forms the crest of a ridge 
 trending N. 65-70° W. and has little or no overburden. 
 The limestone is exposed for a length of 1,800 feet and 
 an average width of 120 feet. A maximum of 200 feet 
 of depth is exposed above the level of Bird Creek but 
 the pendant continues downward for an undetermined 
 distance. Accessible reserves in the lens probably exceed 
 1,000,000 tons. A few small granitic dikes penetrate the 
 limestone but are not believed to be a serious problem in 
 quarrying. Most of the limestone is white rather than 
 colored. The following analyses on samples collected by 
 the authors and analyzed by Abbot A. Hanks, Inc., are 
 believed to be representative of the variations found in 
 the deposit. 
 
 Sample 
 
 a. p. 1.', 
 
 50.79 
 
 3.89 
 
 .36 
 
 .17 
 
 Oxide 
 
 CaO 
 
 MgO 
 
 SiOa 
 
 FesOa 
 
 A1,.0 3 
 
 P.Os 
 
 Remainder _. 
 (chiefly CO») 
 
 Sample 
 G.P. 13 
 . 54.4S 
 _ 3.43 
 . 1.74 
 . .19 
 . .29 
 . .05 
 . 39.82 
 
 .03 
 
 44.51 
 
 Sample 
 
 G.P. 15 
 
 47.80 
 
 6.26 
 
 .58 
 
 .17 
 
 .27 
 
 .02 
 
 44.90 
 
 Sample 
 
 G.P. 16 
 
 52.24 
 
 .73 
 
 3.66 
 
 .23 
 
 .73 
 
 .04 
 
 42.37 
 
 #2 
 
 #3 
 
 #4 
 
 #5 
 
 #6 
 
 #7 
 
 53.18 
 
 55.30 
 
 55.50 
 
 55.45 
 
 55.50 
 
 37.99 
 
 2.13 
 
 0.43 
 
 0.36 
 
 0.54 
 
 0.35 
 
 14.83 
 
 0.25 
 
 0.25 
 
 0.30 
 
 0.35 
 
 0.2 
 
 0.1 
 
 0.30 
 
 0.10 
 
 0.35 
 
 0.35 
 
 0.25 
 
 0.20 
 
 44.13 
 
 43.90 
 
 43.96 
 
 44.10 
 
 43.25 
 
 46.77 
 
 95. 
 
 98.7 
 
 99.1 
 
 99.0 
 
 99.1 
 
 68.0 
 
 Seven other samples collected and analyzed by the 
 owner, Howard Harris, a trained chemist, yielded the 
 following results. The best of these probably indicate the 
 maximum quality of rock available in the deposit. 
 Oxide # 1 
 
 CaO 54.76 
 
 MgO 0.79 
 
 Si0 2 0.30 
 
 Fe,<> 3 0.25 
 
 AUOa 
 
 COo 44.69 
 
 CaCOa 97.7 
 
 Bird Canyon Ledge (13) 
 
 In 1925 the Old Mission Portland Cement Company, 
 one of the predecessors to Ideal Cement Company, ex- 
 plored the Bird Canyon Ledge deposit and acquired the 
 mineral rights on it. A geologic map was made by Bailey 
 and Robin Willis and some drilling was done with the 
 idea of adding to the cement-rock reserves for the plant 
 at San Juan Bautista. Ideal Cement Company still holds 
 the mineral rights, but the deposit remains undeveloped. 
 It is located 3| airline miles east of Fremont Peak on 
 the upper reaches of the main fork of Bird Creek at its 
 confluence with one of its unnamed tributaries. The de- 
 posit is accessible from the paved Fremont Peak road by 
 way of the Reeves ranch road and Bird Canyon jeep 
 trail, but is 14 miles by road from the cement plant at 
 San Juan Bautista. This distance could be materially 
 shortened by construction of a road from San Juan 
 Canyon up Bird Creek. 
 
 The Bird Canyon Ledge occupies the south slope of a 
 ridge trending N. 65° E. The north border of the prin- 
 cipal limestone mass lies close to the ridge crest. The 
 south border, which is more irregular, lies close to the 
 

 CALIFORNIA DIVISION OF MINES 
 
 [Special Report 56 
 
 canyon bottom. In plan the deposit is about 600 feet 
 long parallel to the ridge and 800 feet long perpen- 
 dicular to the ridge. From ridge crest to creek bottom, 
 a depth of 560 feet of limestone is exposed. The predom- 
 inating surface trace of well-developed joints in the 
 limestone strikes X. 55-60° E. and the joint surfaces dip 
 very steeply southeast, but it is doubtful if this repre- 
 sents bedding. Bonafide bedding was not observed in 
 I he main mass. The limestone is bounded on the north 
 and south by quartz-mica schist and granite; on the east 
 by granite; and on the west by a mass of gray replace- 
 ment silica. From exposures seen along the creek the 
 deposit bottoms in granite and silica and the chances of 
 it continuing down below the level of the creek bottom 
 are small. Roughly 10,000,000 tons of carbonate rock are 
 present in the main mass but there is some question as 
 to whether all of this is suitable for manufacture of 
 Portland cement. 
 
 The old Willis map shows the locations of six drill 
 holes, but the cement company was unable to find a rec- 
 ord of structure sections or analyses connected with this 
 drilling. Although the surface of the mass does not show 
 the presence of excessive dolomite there is sufficient var- 
 iation among the analyses in the table below to indicate 
 that the magnesium content of the mass as a wdiole may 
 be too high for use in portland cement. 
 
 Middle Dam Deposit (14) 
 
 The Middle Dam deposit is on the Crowe-Harris ranch 
 on the east slope of North Canyon a quarter of a mile 
 northwest of the A. S. and R. deposit. It is undeveloped. 
 A geologic map published by Taliaferro (1948) shows a 
 lenticular, arcuate, northwest-trending mass of lime- 
 stone nearly a mile long and reaching a width of 500 
 feet at the broadest part of the lens. However, the lime- 
 stone is not continuous at the surface within the area 
 shown on the map and contains numerous leaves of schist 
 and granodiorite. Individual masses of mineable lime- 
 stone probably do not exceed 200,000 tons each, although 
 several might be suitable for development. The terrain 
 is rugged. 
 
 The only available analysis was done on a typical 
 sample of the rock collected by Harris and Bowen in 
 lf>54, Abbot A. Hanks, Inc., analysts. 
 
 Remainder, 
 Sample no. SiO- Fe-Os Al-Os CaO MgO P2O5 chiefly CO- 
 OP^ .52 .08 .16 43.17 10.32 Trace 45.7,") 
 
 The analysis shows that at least part of the rock in the 
 lens is dolomitic, although some rock of lower magnesium 
 content might be expected in the deposit. 
 
 Power Line Deposits (15) 
 
 The Pow-er Line deposits are 9 airline miles southeast 
 of San Juan Bautista on the Reeves ranch at the head- 
 waters of the Bird Creek drainage. They lie on the divide 
 between Bird and Swamp Creeks. Mineral rights are 
 held by either Ideal Cement Company or Dr. Rollin 
 Reeves. The deposits are accessible by improved dirt road 
 via the Fremont Peak and Reeves Ranch roads. 
 
 Limestone crops out over rolling terrain suitable for 
 ordinary quarrying operations. Reserves total many mil- 
 lions of tons, but so far as the authors know have not 
 been explored or tested. On surface outcrop the limestone 
 is medium-coarse-grained, light blue-gray rock without 
 apparent large dolomite replacement masses. Although 
 somewhat remotely situated, the Power Line deposits 
 are sufficiently large to warrant exploration and testing 
 for possible use in portland cement or for general chem- 
 ical use. 
 
 Upper Bird Creek Deposit (16) 
 
 The Upper Bird Creek limestone mass is on the west 
 side of Bird Creek Canyon a quarter of a mile south of 
 the Bird Canyon Ledge, or nearly midway between the 
 Bird Canyon Ledge and Power Line deposits. It is on 
 the Reeves ranch, but mineral rights are probably held 
 by Ideal Cement Company. 
 
 In plan this deposit is shaped like a T-bone steak 
 with the longest axis trending northwest. It is about 
 1,600 feet long, 800 feet in maximum width, and has 
 been exposed to a depth of over 400 feet. Most of the 
 rock is medium-grained, blue-gray material suitable for 
 
 Analyses of samples from ihe Bird Canyon Ledge. 
 
 Sample number 
 
 CaO 
 
 MgO 
 
 Si0 2 
 
 Fe203 
 
 AI2O3 
 
 P2O5 
 
 Na 2 
 
 K2O 
 
 Ignition loss 
 (chiefly CO2) 
 
 G-21 51.20 
 
 G-22 50.00 
 
 G-23 35.60 
 
 G-24 41.70 
 
 G-25... 39.00 
 
 G-26 39.10 
 
 G-42 53.93 
 
 G-43 54.83 
 
 G-44 43.38 
 
 G-45 46.17 
 
 G-46 42.29 
 
 G-47 36.86 
 
 G-48 40.64 
 
 44.74 
 
 29.64 
 
 34.63 
 
 38.00 
 
 50.95 
 
 35.88 
 
 49.45 
 
 3.25 
 
 7.36 
 
 3.26 
 
 3.72 
 
 17.54 
 
 9.96 
 
 14.94 
 
 2.12 
 
 19.13 
 
 4.86 
 
 13.74 
 
 4.00 
 
 1.21 
 
 0.80 
 
 0.80 
 
 0.10 
 
 0.15 
 
 17.90 
 
 7.84 
 
 0.81 
 
 7.38 
 
 6.22 
 
 13.95 
 
 3.72 
 
 4.45 
 
 6.04 
 
 6.79 
 
 4.24 
 
 18.57 
 
 7.06 
 
 17.54 
 
 0.12 
 
 11.37 
 
 6.04 
 
 1.91 
 
 3.52 
 
 16.78 
 
 0.28 
 
 5.34 
 
 0.32 
 
 0.19 
 0.23 
 0.73 
 0.12 
 0.39 
 0.53 
 0.05 
 0.05 
 0.02 
 0.03 
 0.25 
 0.13 
 0.16 
 0.14 
 0.17 
 0.03 
 0.03 
 0.02 
 0.02 
 0.01 
 
 0.39 
 0.35 
 0.89 
 0.22 
 0.51 
 1.05 
 0.20 
 0.02 
 3.67 
 0.21 
 1.80 
 0.70 
 0.68 
 1.16 
 0.83 
 0.03 
 1.79 
 0.42 
 0.12 
 0.07 
 
 N. D* 
 
 0.14 
 
 0.05 
 
 37.88 
 
 N. D* 
 
 0.09 
 
 0.03 
 
 42.21 
 
 N. D* 
 
 0.05 
 
 0.05 
 
 34.27 
 
 N. D* 
 
 0.03 
 
 0.01 
 
 39.68 
 
 N. D* 
 
 0.03 
 
 0.01 
 
 34.66 
 
 N. D* 
 
 0.05 
 
 0.10 
 
 39.68 
 
 0.03 
 
 N. D. 
 
 N. D. 
 
 43.78 
 
 0.27 
 
 N. D. 
 
 N. D. 
 
 43.93 
 
 0.01 
 
 N. D. 
 
 N. D. 
 
 34.87 
 
 0.01 
 
 N. D. 
 
 N. D. 
 
 44.93 
 
 0.17 
 
 N.D. 
 
 N. D. 
 
 41.89 
 
 0.10 
 
 N. D. 
 
 N. D. 
 
 44.54 
 
 0.14 
 
 N. D. 
 
 N. D. 
 
 41.89 
 
 0.56 
 
 N. D. 
 
 N. D. 
 
 42.37 
 
 0.10 
 
 N. D. 
 
 N. D. 
 
 47.63 
 
 0.02 
 
 N. D. 
 
 N. D. 
 
 42.70 
 
 0.07 
 
 N. D. 
 
 N. D. 
 
 43.02 
 
 0.16 
 
 N. D. 
 
 N. D. 
 
 46.91 
 
 0.01 
 
 N. D. 
 
 N. D. 
 
 44.78 
 
 0.03 
 
 N. D. 
 
 N. D. 
 
 
 one. 
 
 6 were analyzed by L. A. Caetano, Ideal Cement Company, San Juan Bautista. Samples G-42 through G-55 by 
 -San Francisco. 
 
1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 33 
 
 Portland cement, but a dolomite streak crosses the north- 
 west end of the mass and the deposit would have to be 
 thoroughly tested by drilling to establish whether the 
 mass as a whole is sufficiently low in magnesium. Five to 
 10 million tons of limestone could probably be developed 
 in the Upper Bird Creek deposit. The following analyst's 
 done by L. A. Caetano, courtesy Ideal Cement, on type 
 samples collected by Gray are representative of most 
 of the deposit : 
 
 
 
 
 
 
 
 
 
 Ignition 
 
 Sample no. 
 
 SiOs 
 
 FerOa 
 
 Al . 
 
 CaO 
 
 Mi)0 
 
 K,0 
 
 Na : 
 
 loss 
 
 G-16 
 
 .38 
 
 .12 
 
 .18 
 
 55.4 
 
 .35 
 
 .03 
 
 .10 
 
 43.65 
 
 G-17 
 
 .50 
 
 .12 
 
 .12 
 
 54.S 
 
 .54 
 
 .03 
 
 .04 
 
 43.6S 
 
 G-18 
 
 .88 
 
 .08 
 
 .10 
 
 50.2 
 
 4.38 
 
 .03 
 
 .05 
 
 44.18 
 
 G-19 
 
 1.28 
 
 .11 
 
 .13 
 
 54.0 
 
 .39 
 
 .05 
 
 .13 
 
 43.34 
 
 G-20 
 
 .98 
 
 .15 
 
 .17 
 
 54.2 
 
 .35 
 
 .05 
 
 .05 
 
 43.26 
 
 Cienega- Vineyard District 
 
 The Cienega-Vineyard district adjoins the Bird Can- 
 yon district on the southeast. Most of the deposits lie 
 along the west side of Cienega Road between Cienega 
 Valley and Bird Creek 6 to 9 miles southeast of Hollister. 
 Both commercial dolomite and commercial limestone de- 
 posits are found in the district, as well as mixed deposits 
 of no present economic importance. The chief product 
 quarried at present is white crystalline dolomite. Both 
 medium-grained and coarse-grained deposits are avail- 
 able. The carbonate-rock deposits lie largely on the 
 Crowe-Harris, Martin, Beeves, and Hamilton ranches. 
 
 Garner- Harris Deposits (17) 
 
 The Garner-Harris deposits are a series of discontin- 
 uous masses of limestone and dolomite on the Garner- 
 Harris ranch three-quarters of a mile west of Vineyard 
 School. The property is adjacent to the Kaiser-Harris 
 dolomite deposit on the north. The property is owned 
 by Howard Harris, 7800 Cienega Road, Hollister. 
 
 The limestone bodies crop out at or near the crest of 
 an east-trending ridge. Their exact outline is obscured 
 by soil and vegetation. Much of the limestone is brec- 
 ciated, but not badly contaminated by impurities. Coarse- 
 grained grayish-white and medium-grained bluish-gray 
 rocks are the most common types. The masses are partly 
 developed by trenching and test pits which indicate that 
 several hundred thousand tons of rock could be selec- 
 tively mined. Schist interbeds and granitic intrusions 
 interfere with quarrying and some stripping of these ma- 
 terials would be necessary to fully exploit the masses of 
 limestone. The limestone and dolomite masses commonly 
 are separate and only a few masses of mixed rock were 
 conspicuously exposed. Four type samples collected by 
 Harris and Bowen in 1954 yielded the following analyses 
 (Abbot A. Hanks, Inc., analysts) : 
 
 Remainder, 
 Sample no. S1O2 FtiOi AI2O3 CaO MgO P1O5 chiefly COj 
 
 GP-17 1.44 .1!) .67 53.5 .69 .02 43.49 
 
 GP-18 1.76 .21 .33 54.2 .51 .01 42.08 
 
 GP-19 1.18 .34 .36 54.0 .46 .03 43.03 
 
 HU 1 .32 .11 .10 25.0 26.16 .02 48.29 
 
 Photo 29 General view of the Westvaco Chemical Division of Food Machinery and Chemical Corporation operation near 
 
 Vineyard, San Benito County. 
 

 I 
 
 <r 
 
 
1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 35 
 
 Photo 30. (opposite). Dolomite crushing and sizing installa- 
 tion at the Vineyard quarries of the Westvaco company. 
 
 Kaiser- Harris (Permanente) Dolomite Deposit (18) 
 
 Kaiser Aluminum and Chemical Company owns a 
 dolomite deposit near the corner common to the Martin, 
 Reeves, McCray and Garner-Harris ranches about 2 
 miles southwest of Vineyard Winery. It was purchased 
 from Cassie Crowe and Howard Harris in 1943 after an 
 extensive trenching and diamond-drilling program had 
 been completed by the company. 
 
 Coarse-grained, pure-white crystalline dolomite is ex- 
 posed in a series of bulldozer trenches cut into a len- 
 ticular pendant having irregular boundaries. The long 
 axis of the pendant, which is oriented northeast, is at 
 least 1,000 feet long and the width of the mass at its 
 broadest point exceeds 400 feet. The mass has been ex- 
 posed by erosion to a depth of 140 feet. Reserves total 
 several million tons. 
 
 An analysis of a typical sample, collected by Harris 
 and Bowen in 1954 and analyzed by Abbot A. Hanks, 
 Inc., yielded the following result : 
 
 Remainder, 
 Sample no. SiO- Fe.'Cb Ab0:< CaO MgO P.O.-. chiefly COa 
 
 G.P. 23 .14 .11 .17 30.80 22.13 Trace 47.63 
 
 Martin Ranch Deposits (19) 
 
 There are several limestone and dolomite deposits in 
 the southeast corner of the E. L. Martin ranch, which 
 corners on the Kaiser-Harris dolomite property 2 miles 
 southwest of Vineyard School. The largest dolomite 
 
 deposit was explored to some extent by Westvaco Min- 
 eral Products Division of Pood Machinery and Chemical 
 Corporation in 1956. Although reserves are not yet 
 proven, this pendant is both large and uniform and 
 ultimately will probably be developed for refractory dol- 
 omite. 
 
 Although the boundaries of the dolomite pendant are 
 obscured by soil cover and vegetation, the mass is at least 
 1,200 feet long and 200 feet wide. The long axis of the 
 deposit trends northwest over a slope favorable for 
 quarrying. Five or six bulldozer cuts spaced 50 to 100 
 feet apart have uncovered uniform, coarsely crystalline, 
 white dolomite. The mass lias been exposed by erosion 
 to a depth of at least 300 feet. 
 
 
 
 
 
 
 
 
 
 Remainder, 
 
 Sample 
 
 no. 
 
 SiOj 
 
 Fej0:i 
 
 AIlO:> 
 
 CaO 
 
 MgO 
 
 P.O. 
 
 chiefly CO- 
 
 M.I). 
 
 1 
 
 .2(i 
 
 .02 
 
 .00 
 
 2!).7."> 
 
 22.19 
 
 .02 
 
 46.70 
 
 M.D. 
 
 o 
 
 .is 
 
 .05 
 
 .04 
 
 20.r>7 
 
 22.35 
 
 .02 
 
 47.79 
 
 M.D. 
 
 3 
 
 .44 
 
 .01 
 
 .OS 
 
 20.71 
 
 22.13 
 
 .01 
 
 47.02 
 
 M.D. 
 
 4 
 
 .32 
 
 .0(1 
 
 .10 
 
 29.91 
 
 21.98 
 
 .03 
 
 47.00 
 
 McCray Ranch Deposits (20) 
 
 The McCray ranch borders the Kaiser dolomite prop- 
 erty on the south and parts of the carbonate-rock pend- 
 ant extend south into the McCray property. The McCray 
 ranch is owned by Dr. Rollin Reeves of Salinas. 
 
 Although not well exposed, the white dolomite of the 
 Kaiser deposit apparently extends onto the McCray 
 ranch. The lobes of limestone that extend onto the Mc- 
 Cray property are not extensive and presence of dolo- 
 mite of commercial grade is improbable. Much of the 
 limestone, however, appears to be of good quality as 
 
 Photo 31 (helow). Quarry benches in snow-white, crystalline dolomite at Westvaco's Vineyard quarries. Pendants of dolomite are 
 suspended in granitic rock and schist. Granitic intrusions offer some hindrance to quarry management but part of this cost is offset by 
 the broken character of the rock. The quarry is close to the San Andreas fault zone and the deposit was well broken up prior to the time 
 of quarrying. 
 
 ■ 
 
 f r 
 
 v_ 
 
36 
 
 CALIFORNIA DIVISION OP MINES 
 
 [Special Report 56 
 
 
 Photo 32. Closeup of quarry-run crystalline dolomite at Westvaco's Vineyard quarries. 
 
 shown in the following analyses done on type samples 
 collected by Harris and Bowen in 1954 and analyzed by 
 Abbot A. Hanks, Inc. : 
 
 Remainder, 
 Sample no. SiOs Fe.O AI2O3 CaO MgO P2O5 chiefly CO ■ 
 
 GP-20 .20 .15 .19 54.44 .66 .02 44.34 
 
 GP-21 .34 .09 .27 54.80 .54 .03 43.97 
 
 Palmtag-Harris Ranch Deposits (21) 
 
 Several lenses of limestone are present on the old 
 Palmtag property now owned by Howard Harris of Hol- 
 lister. These deposits are about half a mile southwest of 
 Vineyard School. 
 
 The principal mass of limestone occurs as an irregular 
 lens-like pendant, the long axis of which trends about 
 X. 70° W. It is roughly 2,000 feet long by 400 feet wide 
 and is exposed to a depth of over 120 feet. Several mil- 
 lion tons of carbonate rock are present, but the relative 
 abundance of calcitic and dolomitic strata in the mass 
 has not been adequately determined. The stratification, 
 although crudely developed, appears. to strike northwest 
 and to dip steeply northeast. Dolomitic strata appear to 
 be most abundant in the southwestern or lower part of 
 the section. The limestone is medium to coarsely crystal- 
 line and is chiefly blue-gray with faint banding. 
 
 The following table of analyses done on random 
 samples taken by Harris and Bowen in 1954 and 1957 
 give some idea of what range of chemical composition 
 is likely in the mass. The single dolomite sample HHP-10 
 was hand-picked from one thin band and is not represent- 
 ative of a significant volume of rock. Analyses are by 
 Abbot A. Hanks, Inc., of San Francisco. 
 
 
 
 
 
 
 
 
 Remainder 
 
 Sample no. 
 
 SiOa 
 
 Fe-03 
 
 AI2O3 
 
 CaO 
 
 MgO 
 
 P2O5 
 
 chiefly CO 
 
 HHP-1 
 
 1.22 
 
 .15 
 
 .48 
 
 53.72 
 
 .46 
 
 .02 
 
 43.95 
 
 HHP-2 
 
 .61 
 
 .15 
 
 .30 
 
 54.45 
 
 .69 
 
 .01 
 
 43.79 
 
 HHP3 
 
 .59 
 
 .11 
 
 .31 
 
 54.49 
 
 .75 
 
 .02 
 
 43.73 
 
 HHP-4 
 
 .25 
 
 .11 
 
 .26 
 
 54.67 
 
 .69 
 
 .07 
 
 43.95 
 
 HHP-5 
 
 6.59 
 
 .18 
 
 1.34 
 
 49.60 
 
 .60 
 
 .02 
 
 41.67 
 
 HHP-6 
 
 .84 
 
 .11 
 
 .44 
 
 54.49 
 
 .48 
 
 .03 
 
 43.61 
 
 HHP-7 
 
 .39 
 
 .29 
 
 .43 
 
 54.90 
 
 .25 
 
 .05 
 
 43.69 
 
 HHP-8 
 
 2.06 
 
 .29 
 
 .69 
 
 53.40 
 
 .45 
 
 .02 
 
 43.09 
 
 HHP-9 
 
 2.34 
 
 .22 
 
 .81 
 
 51.56 
 
 1.90 
 
 .11 
 
 43.06 
 
 HHP-10 
 
 ___ .28 
 
 .09 
 
 .09 
 
 30.51 
 
 21.44 
 
 .02 
 
 47.57 
 
 Reeves Northeast Deposits (22) 
 
 The Reeves Northeast deposits are in the northeast 
 corner of the Reeves ranch where it corners on the Mar- 
 tin, McCray, and Kaiser properties. The principal mass 
 is probably the northwest extension of the pendant 
 which crops out on the Kaiser and McCray properties, 
 but the boundaries of this mass have not been mapped. 
 
 Blue-gray, medium and coarse crystalline limestone 
 without overburden, crops out along the summit of a 
 northwest-trending ridge. The beds have a general east 
 strike and steep north dip. No patches of dolomite were 
 noticed in the exposures examined and no granitic intru- 
 sions were seen. Several million tons of limestone could 
 probably be developed. Only one analysis is available, 
 done on a type sample collected by Harris and Bowen 
 in 1954. The analysis is by Abbot A. Hanks, Inc., of 
 San Francisco : 
 
 Remainder, 
 Sample no. SiOs re . Al 0: CaO MgO P. -Or. chiefly CO2 
 
 G.P. 22 1.56 .17 .95 52.67 1.41 .03 44.21 
 
1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 37 
 
 Westvaco (O'Hara Ranch) Deposit (23) 
 
 The quarries of the Westvaco deposit are a prominent 
 landmark in the hills just southwest of Vineyard Win- 
 ery. They were opened in 1947 by the present owners, 
 the Westvaco Mineral Products Division of Food Ma- 
 chinery and Chemical Corporation, to supply the chem- 
 ical plant at Newark. Since that time the quarries have 
 produced roughly a million tons of high-grade dolomite. 
 Prior to 1947 small tonnages of dolomite had been quar- 
 ried from time to time — some as early as 1915. 
 
 "White, medium crystalline dolomite occurs in a north- 
 west-elongated mass roughly oval in plan. The mass is 
 at least 1,800 feet long and 600 feet wide and has been 
 explored to a depth of nearly 200 feet. It is enveloped 
 in deeply weathered schist and granitic rock and granitic 
 intrusions penetrate the dolomite in several places. The 
 deposit is in or close to the San Andreas fault zone 
 and the dolomite has been thoroughly crushed through- 
 out the deposit. This lowers the cost of quarrying but 
 raises the proportion of waste material. Several million 
 tons of usable rock were proved. Further exploration 
 was being done during the summer of 1958. According 
 to the company the rock runs close to the theoretical 
 composition for dolomite — slightly over 21 percent MgO. 
 Iron oxide stains along the fracture surfaces are the only 
 visible impurity. Logan (1947, p. 278) lists an analysis 
 made by Smith-Emery Company from a sample col- 
 lected toward the north end of the mass from a quarry 
 then operated by A. E. Hamilton, which is probably 
 representative of the deposit : 
 
 SiOs 
 
 Abth 
 
 FtjOi 
 
 CaO 
 
 MgO 
 
 Mn 
 
 CO? 
 
 .17 
 
 .36 
 
 .11 
 
 31.00 
 
 21.23 
 
 .006 
 
 47.30 
 
 Hartnell District (24) 
 
 The Hartnell district, which adjoins the Natividad 
 district on the south end, lies 5 to 7 miles east of Salinas. 
 The geologic map of C. L. Herold, made in 1934 as part 
 of a graduate thesis at the University of California, de- 
 lineates a large number of limestone pendants scattered 
 over an area of 40 or 50 square miles. Most of these are 
 on the J. C. Bardin ranch and Barnes ranches. 
 
 Pendants in the Hartnell district that were examined 
 by the authors were found to consist either of inter- 
 mingled dolomite and calcite rocks or of carbonate rocks 
 intermingled with granitic rocks and with quartz-mica 
 schist. Although small masses of white limestone and 
 white dolomite of acceptable continuity and satisfactory 
 commercial quality probably can be developed in the 
 Hartnell district, it is doubtful if many of these exceed 
 200,000 tons; many would be much smaller. One small 
 quarry on the old Hartnell College property once yielded 
 limestone for construction purposes, but this has not 
 been operated recently. 
 
 Bluerock Mountain-Quail Creek Deposits (24a) 
 
 These are on the Barnes ranch (formerly the Norvel 
 and Silacei properties) on Old Stage Road 8 miles south- 
 east of Salinas and 3 to 6 miles northeast of Chnalar. The 
 Bluerock Mountain deposit lies on the west slopes of the 
 mountain on rugged topography. It is an oval mass 
 having a slight east elongation and underlies most of 
 the SW| sec. 25, T. 14S., R. 4E., M.D. It has not yet been 
 sampled or otherwise explored. Most of the mass appears 
 
 to be medium crystalline, blue-gray limestone. Reserves 
 probably aggregate many millions of tons. 
 
 The Quail Creek deposit was under development in 
 May, 1959, by Barnes Construction Company of San 
 Marino, California, as a source of roofing granules and 
 industrial limestone. A small quarry at the northwest 
 end of the deposit was worked as a source of material 
 for lime early in the 1900 's. The main mass is a sheet- 
 like pendant set on edge striking N. 65-75°W. and dip- 
 ping 22-45°SW. It forms a blanket (dip slope) on the 
 west slope of the ridge. The thickness of the sheet varies 
 from 120 feet in the center of the mass to less than 50 
 feet at the northwest end. The limestone is enveloped 
 in granitic rock and schist and granite dikes penetrate 
 the mass in numerous places. The northwest end of the 
 deposit consists of mixed limestone and dolomite but the 
 southeasterly two-thirds appears to be principally lime- 
 stone. Most of the deposit has been stripped of its thin 
 overburden of soil and caliche and has been thoroughly 
 explored by trenching, rotary drilling and diamond- 
 drilling. More than 2,000,000 tons of rock have been 
 blocked out, but because of granitic intrusions and dis- 
 coloration patches, recovery may run less than 50%. The 
 CaC0 3 content may be expected to vary from 96% to 
 less than 60%. The proportion of high-grade to marginal 
 and sub-marginal-grade rock has not been determined. 
 
 Mount Harlan-McPhails Peak District 
 
 Limestone masses of many different sizes are found in 
 the Mount Harlan vicinity west of Cienega Valley be- 
 tween Pescadero Canyon and McPhails Peak. A number 
 of these have long been held by commercial firms as 
 potential sources of commercial limestone, and ruins of 
 several lime kilns operated prior to 1910 are found in 
 the district. As the deposits are more remotely situated 
 from markets and from rail transportation than those 
 to the north and west, there has been less incentive to 
 develop them. Dolomite deposits of notable size have 
 thus far not been found. The pure white crystalline de- 
 posits are the most likely to be used in the near future. 
 None of the limestone deposits are believed to be large 
 enough to support a cement plant of comparable size to 
 most operating in California. 
 
 Cowell-Thompson Creek Deposit (25) 
 
 For more than 50 years the Henry Cowell Lime and 
 Cement Company held this deposit and it once supported 
 a bank of large lime kilns. Deposit and kilns are conspic- 
 uous landmarks on the north side of Thompson Creek 
 Canyon, 3 miles by road southwest of Cienega School. 
 The property is administered by the Henry Cowell Trust 
 Estate, 2 Market Street, San Francisco, California. 
 
 The deposit is a thin, sheet-like pendant, set on edge, 
 60 to 100 feet wide and nearly half a mile long. It crops 
 out over very steep topography, between granite and 
 schist wall rocks. The long axis of the mass trends almost 
 due west and the strata dip very steeply north. Granite 
 sheets and quartz-mica schist interbeds are found at nu- 
 merous places within the limestone. Because of the 
 thinness and attitude of the limestone mass, much of it 
 would have to be mined underground. Dolomite was not 
 observed in the deposit and most of the rock appears 
 to be medium to coarsely crystalline white or blue-gray 
 limestone low in impurities. Analyses are not available. 
 
38 
 
 CALIFORNIA DIVISION OF MINES 
 
 [Special Report 56 
 
 Photo 33. Old lime kilns and quarry at the Cowell Thompson Creek deposit in the Mt. Harlan district about 16 miles 
 
 by road south of Hollister. 
 
 The pendant contains several millions tons of limestone 
 but selective mining would be necessary to maintain a 
 uniform grade of rock. 
 
 Hamilton, Harlan, Mayries, and McPhail Deposits (26) 
 
 The Hamilton, Harlan, Mayries, and McPhail are ad- 
 joining properties clustered together on and to the north- 
 cast of Mount Harlan. They are in sections 13, 14, 22, 
 23, and 24, T. 14 S., R. 6 E.,' M.D. The disposition of the 
 property boundaries is not known to the authors. A good 
 dirt road connects with the properties by way of the 
 Thompson Creek and Cienega Valley roads. A. E. Ham- 
 ilton, Box 621, Hollister, is reported to have done devel- 
 opment work at one of the deposits during 1956. 
 
 The most promising deposit, which consists of pure 
 white, coarsely crystalline limestone without visible im- 
 purities or serious discoloration, lies close to the bound- 
 ary common to the SW^ sec. 14 and the NW^ sec. 23. 
 The rock crops out on a hill, occupying 5 or 10 acres, 
 but the exact size and shape of the mass is not known 
 to the authors. A small quarry, from which a few thou- 
 sand tons of material has been removed, evidently sup- 
 plied the bank of kilns which lie close to the Harlan 
 Creek road northwest of the quarry. The extent of out- 
 crops suggests that there may be half a million to a 
 million tons of limestone in the mass, but it would have 
 to be selectively mined because of the prevalence of gra- 
 nitic intrusions. This deposit is attractive as a source of 
 high-calcium, pure white limestone for glass and for 
 ialty products. 
 ■ Hamilton deposit, on the south slope of Mount 
 Harlan, is a lenticular, east-striking, south-dipping mass 
 
 about 1,000 by 3,000 feet as seen in plan. It may contain 
 as much as 20,000,000 tons of carbonate rock. The fol- 
 lowing mean analysis is the composite of 33 samples 
 taken at 5-foot intervals perpendicular to the strike of 
 the main part of the mass. 
 
 CaO '- 52.22 
 
 MgO 2.60 
 
 SiOs 0.75 
 
 RaOa 0.64 
 
 Loss on ignition 44.79 
 
 Logan (1947) lists an analysis of a sample taken from 
 the Hamilton property and analyzed by Smith-Emery 
 Company of Los Angeles : 
 
 SiOa 0.14 
 
 AlsOa 0.10 
 
 Fe 2 3 0.02 
 
 CaO 54.19 
 
 MgO 0.84 
 
 Loss on ignition 44.34 
 
 Calculated as CaCOa 96.72 
 
 There are other masses of white and blue-gray limestone 
 in the five sections listed above, but most of these are un- 
 developed and untested. 
 
 Westphal Ranch Deposits (27) 
 
 These deposits are on the south slopes of Mt. Olds 9 
 miles east of Chualar in sees. 10 and 11, T. 15 S., R. 5 E., 
 M.D. They are owned by the Herald Ranch, a trust es- 
 tate, Herb G. Meyer, 16 San Pedro St., Salinas, Califor- 
 nia, manager. The beds are sinuous but have a general 
 east strike and a steep south dip. The carbonate rocks are 
 
1959] 
 
 LIMESTONE AND DOLOMITE, NORTHERN GABILAN RANGE 
 
 39 
 
 
 
 Photo 34. The western portion of Roeky Ridge, observer facing west, showing white dumps of the barite workings. Be- 
 tween 1016 and 1920 about 2,700 tons were mined from veins in this vicinity that yielded $31,000. 
 
 interbeddecl with quartz-mica schist and quartzite, and 
 some skarn-rock has developed along granitic contacts. 
 None of the lenses exceed 200 feet in width and they are 
 scattered along more than a mile of strike length. The 
 rock is medium-to-coarse-crystalline and blue-gray to 
 nearly white. The chemical variations based upon nearly 
 100 surface samples are indicated in the following table : 
 
 CO and 
 MgO S P Mu RO, HO 
 
 .0-18.2 .01-. 003 .001-. 13 .02-. 06 .54-. 93 42-44 
 
 Fe SiO:. AfeOa CaO 
 .15-.30 .28-5.2 .07-. 63 32.9-53.8 
 
 Because of the heterogeneous nature of the deposit uni- 
 form rock can only be obtained in masses containing less 
 than 1,000,000 tons each; many are much smaller than 
 this. 
 
 Willow Creek District (28) 
 
 Wilson's (1943) geologic map of San Benito quad- 
 rangle shows two elongated masses of limestone in the 
 San Andreas fault zone just west of the county road 
 and the San Benito River between Willow Creek and 
 Jungle Inn. According to Logan (1947, p. 274), most 
 of the limestone is on the George Mendeley ranch in 
 the Wi sec. 27, T. 15 S., R. 7 E., M.D. 
 
 The limestone extends along the county road in a 
 northwesterly direction for over a mile and reaches a 
 thickness of 400 or 500 feet. The rock has been thor- 
 oughly brecciated in the San Andreas fault zone but in 
 general has been firmly re-cemented. It is medium- 
 grained, blue-gray or blue-gray and white rock. A single 
 composite sample taken across a 75-foot width of sec- 
 lion near the southern end of the main mass by C. A. 
 Logan in 1946 yielded the following results (Abbot A. 
 Hanks, Inc., of San Francisco, analysts) : 
 
 CaCOa 92.08 
 
 MgC0 3 2.99 
 
 SS :::::::::::::::::::::::::::::::} °- 
 
 Insolubles, chiefly SiOu 4.59 
 
 No development work has been done on the deposit but 
 the surface area underlain by it is large enough to attract 
 a cement company should the above analysis be repre- 
 sentative of the deposit. 
 
 Barite Deposits West of Fremont Peak (29) 
 
 Small deposits of barite have been found in the Fre- 
 mont Peak area extending westward from the peak along 
 the ridge for a distance of nearly 1 mile. An area ap- 
 proximately 800 feet long, beginning about 800 feet 
 west of the peak, has been the most extensively pros- 
 pected. Three northwest-trending adits have been driven 
 into the ridge and there are a number of shallow prospect 
 pits along the south side of the ridge. The eastern part of 
 the deposit lies within Fremont Peak State Park; the re- 
 mainder is on the Bardin ranch. 
 
 According to Bradley and Logan (1917, p. 624) out- 
 croppings on Fremont Peak were investigated as early 
 as 1864 by miners who believed they had discovered 
 silver ore, but who abruptly ceased prospecting when 
 they found no silver. Apparently there was no further 
 development until 1915 when L. II. Day and II. W. Un- 
 derwood of Hollister took an option on the property and 
 made a few shallow prospect cuts. Mr. Day reported 
 that two assays showed 98.6 percent and 99.7 percent 
 barium sulfate. In December 1915, Win. A. Farish Jr. 
 of San Francisco was reported to be opening the prop- 
 erty (Bradley and Logan, op. cit.). This venture marked 
 
II) 
 
 CALIFORNIA DIVISION OF MINES 
 
 [Special Report 56 
 
 k 
 
 Photo 35. Closeup of white crystalline barite in veins and 
 replacement salients cutting gray dolomitic limestone. The veins 
 are developed along a zone of brecciation, probably an old fault 
 zone, which parallels the east side of the crest of Rocky Ridge. The 
 barite-bearing solutions which formed the veins probably were 
 related to the granitic intrusions. A little scheelite is also found 
 along the granitic rock-limestone contact below the barite workings 
 and farther toward the west. 
 
 the beginning of a 5-year period of operation with pro- 
 duction as follows : 
 
 Short tons 
 Year of barite * Value * 
 
 1916 225 $1,373.00 
 
 1917 1226 11,034.00 
 
 1918 100 1,500.00 
 
 1919 1000 15,000.00 
 
 1920 150 2,250.00 
 
 2701 $31,157.00 
 
 • Statistics compiled by C. J. Kundert, January 1956. 
 
 During this 5-year period the Fremont Peak area furn- 
 ished an average of approximately 25 percent of the 
 total recorded barite production in California and in 
 one year, 1918, 100 percent (Bradley, 1921, p. 116). 
 
 By 1920, the property was being operated by A. R. 
 Raskins, llollister, under a lease from Messrs. J. and H. 
 Bardin, Salinas (Boalieh, 1921, p. 156). The material 
 was hauled by truck to the railroad at San Juan Bau- 
 tista, a distance of about 12 miles. This was the last year 
 for which production was reported, and the property 
 has been inactive since. 
 
 The barite is crystalline, white to gray in color, and 
 ranges from fine to coarse grained. It occurs as pods or 
 discontinuous veins which pinch and widen from 2 
 inches or less up to several feet and are complexly 
 interwoven with silicified dolomitic limestone. The barite 
 zones cut across the apparent bedding of the carbonate 
 host rock, which in places is a very cavernous limestone 
 with a notable development of light brown colored drip- 
 stone. 
 
 The barite shows a characteristic banded structure. 
 Well-defined barite vein material replaces dolomitic 
 limestone and fades off into a replacement pattern in 
 the carbonate rock typical of epithermal deposits. Low- 
 temperature mineralization is also indicated by the ab- 
 ut' wollastonite and epidote. 
 principal mining centered in an area about 
 eet west of Fremont Peak. Here an upper adit, 
 
 20 2-59 
 
 stoped to the surface in places, was driven into the ridge 
 from the north side at about N. 30° W. and opens into 
 a large stope, open to the surface, on the south side of 
 the ridge. The stope more or less parallels the ridge and 
 is about 75 feet long, 25 feet wide, and of unknown depth. 
 There is also a lower adit driven in the same direction 
 about 150 feet, which probably was used to pull ore from 
 the stopes. This adit was accessible in August 1955, 
 but in need of some cleaning out. Below the stoped area 
 is a zone of vuggy vein silica, probably a replacement of 
 dolomitic limestone ; dolomitic limestone lies above. 
 Abundant barite and replacement silica, as well as dolo- 
 mitic limestone, were found on the dumps. 
 
 The deposits must have required selective hand mining 
 methods, due to the interwoven nature of the barite, 
 siliceous rock, and dolomitic limestone. Present market 
 requirements are such that ore must be very selectively 
 mined or ordinary mine-run material must be benefi- 
 eiated. However, as reserves exposed in the workings 
 are apparently small, neither course seems feasible. 
 These conditions, coupled with the fact that part of the 
 deposit lies within a state park, make it unlikely that 
 further production will be made from this deposit. 
 
 REFERENCES 
 
 Allen, John E., 1946, Geology of the San Juan Bautista quad- 
 rangle : California Div. Mines Bull. 133, 75 pp. 
 
 Andrews, Philip, 1936, Geology of the Pinnacles National Monu- 
 ment : Univ. California Dept. Geol. Sci. Bull., vol. 24, no. 1, 
 pp. 1-38. 
 
 Aubury, L. E., and others, 1906, Structural and industrial ma- 
 terials of California : California Min. Bur. Bull. 38, pp. 72-73. 
 
 Becker, George F., 1888, Geology of the quicksilver deposits of 
 the Pacific slope: U. S. Geol. Survey Mon. 13, p. 181. 
 
 Boalieh, E. S., 1921, Monterey County : California Div. Mines 
 Rept. 117, pp. 156-157. 
 
 Bowen, O. E. Jr., and Gray, C. H. Jr., 1958, Stratigraphy of 
 the Sur series at Fremont Peak, northern Gabilan Range, Califor- 
 nia [abstract] : Geol. Soc. America Bull., vol. 69, no. 12, pt. 2, 
 p. 1676. 
 
 Bradley, W. W., Barytes : California Div. Mines Bull. 90, p. 116. 
 
 Bradley, W. W., 1930, Barite in California: California Div. 
 Mines Rept. 26, pp. 45-57. 
 
 Bradley, W. W., and Logan, C. A., 1917, San Benito County: 
 California Div. Mines Rept. 15, pp. 616-673. 
 
 Curtis, G. H., Evernden, J. F., and Lipson, J., 1958, Age deter- 
 mination of some granitic rocks in California by the potassium- 
 argon method : California Div. Mines Special Rept. 54, 16 pp. 
 
 Hutton, C. O., 1951, Uranoan thorite and thorian monazite from 
 blacksand paystreaks, San Mateo County, California (abstract) : 
 Geol. Soc. America Bull., vol. 62, no. 12, pi. 2, pp. 1518-1519. 
 
 Lawson, A. C, 1893, The geology of Carmelo Bay, California : 
 Univ. California Dept. Geol. Sci. Bull., vol. 1, no. 1, pp. 1-59. 
 
 Laizure, C. McK, 1925, Monterey County : California Div. 
 Mines Rept. 21, p. 28. 
 
 Logan, C. A., 1947, Limestone in California : California Jour. 
 Mines and Geology, vol. 43, no. 3, pp. 177-351. 
 
 Reiche, Parry, 1937, Geology of the Lucia quadrangle, Cali- 
 fornia : Univ. California Dept. Geol. Sci. Bull., vol. 24, no. 7, 
 pp. 115-168. 
 
 Taliaferro, N. L., 1948, Geologic map of the Hollister quad- 
 rangle : California Div. Mines Bull. 143, pi. 1. 
 
 Trask, P. D., 1926, Geology of the Point Sur quadrangle, Cali- 
 fornia : Univ. California Dept. Geol. Sci. Bull., vol. 16, pp. 119-180. 
 
 Waring, C. A. and Bradley, W. W., 1919, Monterey County : 
 California Div. Mines Rept. 15, pp. 595-615. 
 
 Whitney, J. D., 1865, Report of progress and synopsis of the 
 field work from I860 to 1864-65, pt. 1, Geology of the Coast 
 Ranges, sec. Ill, The Gavilan Range: California Geol. Survey, 
 pp. 159-160. 
 
 Willis, Bailey, and Willis, Robin, 1925, Geologic map of the 
 Bird Canyon Ledge. From an unpublished private report. 
 
 Wilson, Ivan F., 1943, Geology of San Benito quadrangle, Cali- 
 fornia : California Div. Mines Rept. 39, pp. 183-270. 
 
 printed in California state printing office 
 
DIVISION OF MINES 
 
 GORDON 8 OAKESHOTT, CHIEF 
 
 STATE OF CALIFORNIA 
 DEPARTMENT OF NATURAL RESOURCES 
 
 J 
 
 3500 -, 
 
 4 
 
 
 
 
 A' 
 
 + 
 
 A" 
 
 + 
 
 
 
 
 
 A 
 
 3000 - 
 
 
 (its ^^ 
 
 —-l 
 
 Isdo 
 
 ~T~~^- lsd0 
 
 
 
 
 
 
 
 23O0 - 
 ZOOO - 
 
 flr 
 
 "-- 
 
 / 
 
 grs 
 
 grs 
 
 Isdo 
 
 Is 
 
 / 
 
 Isdo 
 / / / 
 
 
 
 
 
 
 
 
 
 grs 
 
 grs 
 
 ■■ i i i ■. i 
 
 1 
 
 ISOO - 
 
 
 
 
 
 
 
 
 
 
 lOOO - 
 
 
 
 
 
 
 
 
 
 
 Contact, dashed where gradational 
 or approximate 
 
 Fault, dashed where approximate 
 
 Granitic rocks-, largely quartz monzonite 
 and gronodiorite 
 
 FEET ABOVE SEA LEVEL 
 
 SECTION A - A - A - A 
 
 500 1000 1500 2000 2500 1000 
 
 
 
 
 /so y 
 
 
 Dip 
 
 and 
 
 str 
 M 
 
 ke of beds or sen 
 
 /«, 
 
 Jointing 
 
 ine or prospect 
 
 stosity 
 
 SCALE IN FEET 
 
 r ;- Limestone with granitic rock and 
 
 ' Isgs 
 
 schist intercalations 
 
 Siliceous limestone and minor dolomite 
 
 Limy siliceous dolomite 
 
 , ; •; s c h .' ; 
 
 Limestone and dolomite 
 
 Quartz mica schist 
 
 Schist and granitic rock 
 
 Pink quartzite 
 
 GEOLOGIC MAP AND STRUCTURE SECTION OF FREMONT PEAK AREA, MONTEREY AND SAN BENITO COUNTIES, CALIFORNIA 
 
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