IN 24 ! C3 I A3 no. 177 ,^v "fc? 1 ] ■"% '^ LlBRARr UNIVEKSITY OF CALIFORNIA DAVIS STATE OF CALIFORNIA GOODWIN I. KNIGHT, Governor DEPARTMENT OF NATURAL RESOURCES DeWITT NELSON, Director DIVISION OF MINES FERRY BUILDING, SAN FRANCISCO 11 GORDON B. OAKESHOTT, Chief SAN FRANCISCO BULLETIN 177 1958 GEOLOGY AND MINERAL RESOURCES OF SANTA YSABEL QUADRANGLE SAN DIEGO COUNTY, CALIFORNIA Price $1.50 LIBRARY UNIVERSITY OF CAI.irORNTA DAVIS The Library of Congress has cataloged this publication as follows: California. Division of Mines. Geology and mineral resources of Santa Ysabel quad- rangle, San Diego County, California. San Francisco, 1958. 39 p. illus., maps (2 fold. col. in pocket) 28 cm. (Its Bulletin 177) Bibliography: p. 39. 1. Geology — California — San Diego Co. 2. Mines and mineral re- sources — California San Diego Co. I. Title. (Series) TN24.C2A3 no. 177 Copy 2. 557.9498 QE90.S116C3 59-62552 Library of Congress CONTENTS Page Letter of transmittal 5 Geology of Santa Ysabcl quadrangle, San Diego County, California, by Richard .Mt'rriatii 7 .Alini's anil mineral resources of Santa Ysabel quadrangle, San Diego County, California, by Richard M. Stewart 21 Reports cited in Bidletin 177 39 Index 41 PLATES Plate 1. Geologic nuij) of the Santa Ysabel ijuadrangle In ])ocket lA. Economic map of the Santa Ysabel ((uadrangle In pocket (3 J To His Excellency The Hoxorable Edmund G. Brown Governor of the State of California Sir: I have the honor to transmit herewith Bulletin 177, Geology and mineral resources of Santa Ysabel quadrangle, San Diego Countj', California, prepared for publication 1958 under the direction of Gordon B. Oakeshott, Chief of the Division of Mines, Department of Natural Resources. The descriptive text is accompanied by a colored geologic map and an economic map, both on a topo- graphic base, a structure map and sections, and numerous photographs. The report represents the work of Richard Merriam of the Department of Geology, University of Southern California, Los Angeles, California. Supplementary to the descriptive geology is a section on the mines and mineral depo.sits prepared by Richard M. Stewart, Mining Geologist with the Division of Mines. The Santa Ysabel quadrangle lies in the north central part of San Diego County. Hydrothermal gold-bearing quartz veins of the Julian district have been the most important mineral resources in the area, but mining activities are limited. The mines here were most active during the period 1870 to 1880 and the value of the total estimated production from the district is between $2,500,000 and $3,000,000. Small tungsten deposits have yielded some ore. Niekeliferous pyrrhotite bodies near Julian have been prospected but the proved reserves are small. Marble has been quarried from deposits interbedded in the Julian schist. This report represents the results of basic geologic studies and should be of value in the development of natural resources within the area. Respectfully submitted, DeWITT nelson. Director Department of Natural Resources (5) - GEOLOGY OF SANTA YSABEL QUADRANGLE SAN DIEGO COUNTY, CALIFORNIA nv Richard Merriam • Photo 1. 2. 4. OUTLINE OF REPORT Page Abstriiot 7 Introduction 7 (Jenernl Reology (i Uock I'nits 9 Julian schist i) Stonewall quartz (iiorite 11 Mixed rocks 11 San Marcos nahhro 12 (ireen Valley tonalite 12 Lakeview Mountain tonalite 13 Bonsall tonalite 14 Emplacement of batholithie rocks 14 Quaternary sediments 14 Structure 15 Julian schist 17 Igneous rock structures 17 Faults 17 Physiosraphy 18 groundwater 19 Geologic history 20 Illustrations Plate 1. Geologic may of the Santa Ysaliel quadrangle In pocket lA. Economic map of the Santa Ysahel quadrangle In pocket Figure 1. Index map showing location of Santa Ysahel quad- rangle 7 'J. Structure map and sections, Santa Y'sabel quad- rangle 16 Julian schist exposed in roadcut on Highway 79 near Julian 9 Julian schist exposed in Chariot Canyon 10 Northeastern slope of Banner Canyon 10 Mixed rocks at contact of Julian schist and Stone- wall quartz diorite, north end Santa Ysabel Valley 11 5. Green Valley tonalite overlain by mixed rocks near Ballenu Valley 1 13 (i. Residual boulders produced by weathering of lake- view Mountain tonalite 13 7. Exjiosure of Pleistocene ( ?) arkose fanglomerate on Warner Ranch 1," 8. Pleistocene ( ?) arkose exposed in road cut north- east of Lake Henshaw 15 9. Trace of Elsinore fault zone at foot of mountain along south shore of Lake Henshaw 17 10. Trace of Elsinore fault zone down Banner Canyon into Rodriguez Canyon 18 11. Elsinore fault zone in Banner Canyon and Rod- riguez Canyon as seen from Julian Ridge 19 ABSTRACT The Santa Ysabel quadrangle lies along the east edge of the composite Peninsular Ranges batholith of Creta- ceous age. The oldest rocks are Triassic ( '?) schists which occur as small roof pendants and as one large body in the vicinity of Julian. Jurassic ( ?) gneissose quartz dio- rite is intimately mixed with much of the schist, the two making a complex into which were intruded various members of the Cretaceous batholith. These intrusions are limited to gabbro and several tonalites. Structural features of the igneous rocks suggest that emplacement may have been accomplished by stoping in some places and by forceful injection in others. Pleistocene (?) continental gravels occur as remnants of a once continuous extensive blanket in the northern portion of the quadrangle. • Department of Geology, University of Southern California, Los Angeles, California. Manuscript submitted tor pulilication 1952. The two most prominent structural features are the Elsinore fault and the San Felipe fault. These and a few minor faults strike northwest. Northeast-striking joints influence the topography locally. The faulting, and, to some extent, sehistosity, lineation, and foliation, are reflected by the topography, which is characterized by northwest-trending valleys and highlands. Some of the latter have summit areas of low relief. Such areas are not at the same altitude and may be explained by faulting, differential resistance of different rock types, or a combination of both. Mining activities, although once extensive, are quite limited. Niekeliferous pyrrhotite and hypothermal gold- quartz veins are the principal types of deposits. Marble interbeds in the schist have been worked but the quarries are idle. Groundwater is probably the most important of the natural resources. San Jose Valley and San Felipe Val- ley are the best situated portions of the area in this respect. In many places faults have had a notable effect on the position of the water table. INTRODUCTION The Santa Y.sabel quadrangle lies in the north-central part of San Diego County, California. The western boundary of the quadrangle is about 30 miles east of the Pacific Ocean and the southern boundary approxi- mately the same distance north of the Mexican border. The area is a 15-minute quadrangle covering more than 200 square miles. Two state highways and a number of fairly good county roads permit access to most of the region. State Highway 78 is the chief east-west road ; Highway 79 crosses the area from the southeast to the northwest. The topography was originally mapped by the U. S. Geological Survey as the Ramona ((uadrangle, scale 1:125,000. Jjater the southeastern ((uarter of this quad- '""R I V E R S 1 d e SAN Dl EGO SAN DIEGO : < 1 a: UJ D_ 5 Bt«'* Tco ■ Fioi'KK 1. Index map showing location of Santa Ysabel quad- rangle. Geology of the Cuyamaca Peak quadrangle was published in Division of Mines Bulletin 1,">9 (ULjl). (7) California Division of Mines [Bull. 177 rangrle was mapped by the U. S. Army on the scale of 1:62,500 with a 100-foot contour interval anfl named the Santa Ysabel quadrangle. The topography is dominated by the northwest trend of the principal valleys and ranges. The most prominent mountain mass, Volcan Mountain, trends in this direc- tion and is paralleled by the principal valley. San Felipe Valley. Elevations on Volcan Mountain range from 4,000 to 5,000 feet whereas the ad.iacent lowlands are about 2,500 feet. Thus relief of 2,000 feet is common. Highest points on the quadrangle are Volcan Mountain, 5,700 feet; North Peak (of the Cuyamaea group of peaks) near the south edge of the area, 6,000 feet ; and San Ysidro Mountains in the northeast corner of the quad- rangle. Lake Henshaw occupies a prominent topographic low in the northwest corner of the quadrangle. The northeast-trending gorge of the San Diego River is the chief feature of the southwest corner of the quadrangle; at elevation 1,000 this is more than 1.000 feet lower than any other major valley. The divide between western drainage to the Pacific Ocean and eastern drainage to the Salton Sea passes through this quadrangle; approximately two thirds of the quadrangle area drains westward. The headwaters of the San Luis Rey River carry off precipitation in the north. The eastern section is drained by San Felipe Creek and its tributaries in Banner Canyon, Chariot Canyon, and others. The drainage in the southwestern portion is divided between Santa Ysabel Creek and the San Diego River, the latter taking the bulk of the runoff. The area lies on the boundary between the semi-arid western and arid eastern regions. Annual precipitation gradually increases from 18 inches in the west to more than 30 inches along the high divide of Volcan Moun- tain and North Peak. Eastward from this line it rapidly decreases to well below 10 inches per year. Temperatures are not extreme over most of the area although snow is common in the highlands in the winter, and summer highs of over 100 degrees are characteristic of the eastern desert region. Most of the hills of the western half of the Santa Ysabel quadrangle are covered by brush composed of manzanita, ehamise, lilac, several varieties of sage, scrub oak, and similar shrubs. The valleys and some of the hills of this section are chiefly open grasslands dotted with live oaks and a few sycamores. The high- divide section north and south of Julian is covered in part by conifers, alders, and deciduous oaks. Where timber is absent brush as described above is the cover. Meadow-like areas in the highlands support various grasses. The desert portions in the east are characterized by a typical desert flora of various cacti, creosote bush, mesquite and a small variety of juniper. With the exception of the vicinity of Julian (popula- tion 500) which is the only town, the area is thinly populated. Numerous very minor settlements of the cross roads type are widespread. Several Indian reserva- tions occupy a total of nearly 10 percent of the area. Much of the remainder is within the limits of Cleveland National Forest. A large part of the quadrangle is utilized for grazing, cattle raising being the largest single industry. Scattered small deciduous orchards and vineyards are of distinctlj^ secondary importance. Two or three small resorts attract a limited number of vacationists. Mapping was done on the U. S. Army topographic base, scale 1 : 62.500, although aerial photographs were used in part. Three groups of photographs are available, two sets made bv the Agricultural Adjustment Adminis- tration and another by the San Diego County A.ssessor's office. A strip along the western part of the quadrangle was first mapped in 1938-39 (Merriam, 1940) on the old Ramona sheet, the onl.v map available at the time. The strip was re-mapped and the remainder of the Santa Ysabel quadrangle completed in 1950-51 on the new topographic base. Previous Grological Work. The earliest geological descriptions of the area are in general reports covering the entire count.v or a large part of the Peninsular Ranges. One of the first published papers was by W. F. Blake (1856), who made a very brief study on a trip from San Felipe Valley to San Diego. In 1888 there appeared a short report b.y W. A. Good- year which was chiefly concerned with mining but also contained a good description of the physiography. Good- year was probably the first to compare the Peninsular Ranges to the Sierra Nevada. H. W. Fairbanks made a reconnaissance survey in 1893. He noted the various rock types encountered on a traverse from Julian to Ramona, recognizing distinct types in what liad previously been lumped as "granite". His dating of the intrusives as "Jurassic or Cretaceous" agrees well with present information. Little further work was published until 1914 when Merrill (1916) wrote a paper on San Diego and Imperial Counties. It is concerned with mining features and little mention is made of the geology of this specific area. An exhaustive report by A. J. Ellis and C. II. Lee on the groundwater of the western part of the county was published in 1!»19. They critically discussed the physiog- raphy; and tliough they studied the sediments in some detail, the.v grouped igneous and metamorphic rocks as "crystalline complex". The first detailed petrographic work was done by F. S. Hudson (1922), who studied an area in the south- ern part of the Santa Ysabel quadrangle and the north- ern part of the Cuyamaea Peak quadrangle. The physiography of a large part of the Peninsular Ranges was studied and described by Sauer (1929), his being the most extensive work on that phase of the region. A restudy of the Cuyamaea and Julian districts by Donnelly (1934) added little to the knowledge of the surface geology but contributed information regarding the gold mines of the region. A paper by the present writer (Merriam 1946) de- scribed the geology of the western part of the Santa Ysabel quadrangle in a reconnaissance fashion. A detailed study of the geology of a small portion of the quadrangle was made by Creasej- (1946) during an investigation of nickel mineralization south of Julian. One of the principal features of this work is the critical examination of the gabbro and related rocks. The most extensive study of any part of the Penin- sular Ranges was made by Larsen (1948) in the Elsinore, wr->H] Santa Ysabei, Quadranole — GEOLOfiv Corona, and San Lnis Roy (luadranfrlos wiiidi lie to till' northwest and west of tlic area witli whieh this pajier is i-oneerned. In addition to a detailed ;j:eolofric map of these quadranfiles, this report inelndes petro^'raphie descriptions and chemieal analyses of many formations also found in the Santa Ysabei quadranf^le The most recent eontribution to the literature on jreolo-ry of the f^eneral region was made by Everliart (I!*.")]) in his rej^ort on the Cuyaniaea Peak ipiadrangle whieh joins the Santa Ysabei sheet alonj; the latter 's southern boundary. This ])aper inelndes an e.xeellent structure map which materially aids in the vinderstand- ing of many a.spects of the crystalline rocks. GENERAL GEOLOGY The Santa Ysabei quadrangle covers part of the Cre- taceous (■omi)osite batholitli of southern and Lower Cali- fornia. Although the limits of this batholith have not been definitely established, it ajijiears that the Santa Ysabei cpiadrangle is on or near its eastern edge. I\Ieta- morphic rocks, principally (juartzite and mica schist, occur as small roof pendants and as one extensive body in the vicinity of Julian. A complex of schist and grano- diorite of pre-batholith age underlies wide areas. This comi)lex has been invaded by several intrusions of granitic rock ranging from gabbro to tonalite. More silicic types are common in parts of the batholith west and south of this area. Post-bathoJith continental sedi- ments blanket much of the northwestern section ; these are older than the Recent alluvial deposits which lie in most of the valleys. Several northwest-striking faults are responsible for the most prominent to])Ographic features, chief of whieh ai-e Yolcan Mountain. San Felipe Yalley, and San Jose Valley (occupied by Lake Henshaw). Well-developed .joints and possibly some faults have produced minor but inimerous northeast-trending valleys. ROCK UNITS Julian Schist Metamor])hic rocks, principally schist, are in a large area in the central and southei'n part of the ((uadrangle, and in small isolated patches throughout the area. These remnants are too small and scattered to permit simple interpretation of the regional structure or stratigraphy. Although some bodies of metamorphic rocks are gener- ally distinct, there are areas of mixed rocks and zones of injection gneiss; thus some segments of the contacts shown on the map accompanying this report are arbi- trary. Quartz-mica schists and related rocks are the dominant rock type of this group although ((uartzite is in appre- ciable ((uantities and amiihibolite is iiresent. The distri- bution of these types does not appear to be .sj-stematic in any way. The structure of the Julian schist is described in this report under the section on structure ; briefly, however, the strikes are mostly northwest, although local devia- tions are common and probably are related to the em- placement of intrusions. The schistosity dips steeply and parallels the original bedding. Quarh.ih . Two types of ipiartzitc occur, massive and laminated. The former is more common west of the Santa Ysabei ((uadrangle. Occurrences here are limited to a few small, reef-like masses. However, pods or lenses of massive (juai-tzite interbedded with schist are wide- spread. Laminated (piartzite grades into (piartz-mica schist. Individual bands range in thickness- from a fraction of an inch to several inches. Jlicaceous layers are respon- sible for the laminated nature of the rocks; even though these ma\' be absent locally, alternate gray and white streaks remain ilistinct. In thin-section the rock is fine to medium granoblastic, sometimes lepidoblastic. Quartz in j)olygonal or rounded grains amounts to more than 80 percent. Microcline is the most common feldspar, al- though orthoclase and andesine may be present. Musco- vite flakes are connnonly found poikilitically enclosed within the feldspar cry.stals. Jlagnetite and garnet are typical accessories. Scltisi. The schist exhibits a much wider variety than do the quartzites. Quartz-biotite-muscovite schists are most common ; other types are quartz-mica-sillimanite schist, gray muscovite-andalusite schist, amphibolite and fissile mica schist. The (piartz-mica schist is commonly streaked or banded white and gray, brown where weathered. Parting is well marked but discontinuous, irregular, and foliated, rather than smooth and slaty. In thin-section, pol.vgonal and sutured grains of (piartz make up at least half of the rock. Plagioclase, ranging from oligoclase to andesine, never exceeds 10 percent of the rock, but it is generally present. Biotite and muscovite are usually present in about equal amounts, but either may greatly predom- inate in individual bands. Zircon, spessartite, and tour- maline are unevenly distributed accessories. X/^.'Ste* I'llOTO ]. Jiili.an schist exposed in roadcut on HiKln\: near Julian. California Division of Mines fBull. 177 Photo 2. .7\ilian schist exposed in Chariot Canyon. This expo- sure is bloekier in appearance than that shown in photo 1. Pholo hll R. M. Steiriirt. Sillinianite is a eommoii mineral tlirouglioiit the meta- morphie roeks. In only a few places is it sufficiently abundant to warrant its use in the rock name. Such roeks are moderately coarse-grained well-foliated schists. Silli- manite, in white bundles 1 or 2 cm long, similarly ori- ented, is best seen on weathered surfaces. Under the microscope the bulk of the rock appears to be tjuartz and muscovite. Sillimanite needles and tufts lying more or less parallel to the schistosity penetrate the quartz and mica. A minor amount of plagioclase (An4o) is pres- ent. Biotite is abundant in some sections. Andalusite rocks are at least as common as sillimanite rocks. Andalusite rocks are exposed in a roadcut 2 miles east of Wynola and on the east side of Julian Ridge between Chariot Canyon and Cuyamaca Reservoir. In hand specimens these rocks are gray, somewhat finer- grained than other varieties of schist, nearly phyllitie and porphyroblastic. Andalusite prisms, 2 or 3 mm thick and several times as long, are sparsely distributed throughout. Thin sections .show the finer material to be quartz, biotite, and muscovite with or without fine needles of sillimanite. The andalusite porphyroblasts are wreathed by muscovite or may be partially replaced by that mineral. Amphibolife. Amphibolite rock makes up less than 10 percent of the metamorphic rocks. It is generally a distinct unit, although inseparable lenses are found in the schist. Exposures of the rock may be seen about a mile northwest of Witch Creek, on the south border of Santa Ysabel Valley, and a mile southwest of Pine Hills. Excepting the last-named outcrop, which is fairly coarse- textured, the typical rock is relatively dense and fine- grained, and has linear structure but poor schistositj'. The color ranges from light gray or green to black. The texture in thin section is medium to fine granoblastic. More than 50 percent of the rock is hornblende with the following optical properties: a 1.665, (3 1.675, y 1.685; Z A C = 20° ; pleochroism, X-pale yellow, Y-olive green, Z-deep bluish green. Varying proportions of quartz and plagioclase (An^o-nn) make up the remainder. Marble. Medium to coarse massive marble crops out in two places on San Ysidro Mountain. Here nearly vertical beds, as much as a few tens of feet in thickness, are intercalated with quartz-mica schist. Origin of the Metamorphic Rocks. The conditions of metamorphism seem to have been principally those of a mesozone regional type, although some highly injected rocks may approach katazone gneiss, and some of the well-laminated gray phyllitie rocks may best be cla.ssed as epizone. In the terminology of Eskola, the roeks range from the epidote-amphibolite facies to the amphibolite facies. As far as could be determined, neither texture nor mineral assemblage bears anj' systematic relation to igneous contacts. With the exception of scattered zones of injection gneiss, contact effects are absent. Dis- tinct zones of sillimanite and andalusite could not be found ; in fact, the two minerals are found together in many rocks. Metamorphism has, of course, largely destroyed the details of primary structures and textures, but the gen- eral nature of the original roeks is still apparent. The massive quartzites were probably thick-bedded sand- stone, some of which may have been arkosic. Laminated (juartzite and quartz-mica schist may originally have been well-bedded sandstones with shaly or tuffaceous interbeds. The andalusite and sillimanite rocks probably represent argillaceous sediments of various types, al- though the possibility of the introduction of alumina is admitted. Marble, of course, resulted from the metamorphism of minor limestone bodies. Age of the Metamorphic Rocks. Because of the al- most total absence of fossils, most estimates of the age of the rocks must be based on lithologic comparison with formations of known age. The cast of a single fossil found as float suggested a Triassic age for the schists of Chariot Canyon (Hudson, ^■^ w* b«««af :• -s-i ". vr ^ Photo 3. Northeastern shipe of Banner Can.von. Volcan Jloun- tain to the ri),'ht. Northwest strike of .Julian schist is iinlicated h.v slislit cohir handin;; on shipe. Edge of schist belt passes just to richt of small hill in <-('nter. I'hoto hi/ R. M. Sleirart. 19,-)8l Santa Ysarei, Qtadhaxole — Geoi.ooy 11 1922, p. IflO). This correlates well with ajre determina- tions made on metasedimentary roeks in the Santa Ana ^Mountains (Larsen 1948, p. 18). However, fossiliferous Jlississippian roeks near "Winehester (Elsinore quad- raneransp of previous use in ttie literature. < ( I'UOTO 4. Mixed rocks at contact of .Tuliaii schist and Stonewall ijuartz diorite at north enil of Santa Vsalie] Valley. is a complex consisting of migmatites, schist bodies ranging from schlieren to streaks a few tens of feet long, and small lenses or ii-regulai- bodies of relatively uncon- taminated (piartz diorite. Mixing appears to have been principally mechanical, the igneous material having been emplaced along planes of scliistosity or having com- pletely engulfed small schist bodies which generally re- tain distinct form and mineral comjiosition. Contacts of the mixed rocks again.st members of the Cretaceous batliolith are generally sharp, whereas those with schist or Stonewall quartz diorite are gradational so that their ])ositions as shown on the geologic map are somewhat arbitrary. Gneissose phases of the Lake- view and Bonsall tonalites locally resemble the mixed rocks, makin}^ contacts difficult to discern. Outcrops of mixed rocks are prominent and well exposed ; areas of several tens — or even of a few hun- dreds of feet — covered by very sparse vegetation or overburden are connn(ui. Such exposures exhibit promi- nent gnei.ssose foliation produced by alignment of bio- tite and hornblende and by banded distribution of light and dark minerals. Parallel to subparallel or braided vertical joints more or less concordant with the ever- present gneissose structure are common. The general attitudes of this strticture are shown on the .structure maji where they may be seen to roughly parallel the principal structural features of the region. They are everywhere parallel to the schist structures but in many places are crosscut by batholithic intrusions. Although .steej) dijis are the rule, some are rather low. The average hand specimen is a coarse- to medium- grained aggregate of (piartz, plagioclase. biotite, and hornblende. Fresh specimens are medium to light gray, but weathei-ing causes the rock to become light reddish brown. In addition to the megascojiic gneis,soid .structure, a textural parallelism is revealed under the microscope. The texture is the result of the bending of biotite flakes, and the crushing and recrystallization of (piartz aii ovorlain l).v mixed rucks ni';ii- Hiilli'iiM \allHy. riiotfj hi/ R. M. Strinnl. sodic plaf^ioulasp. The abundance of poikilitie hornblende and l)i()tire jrrains is evidenee of late readjustments. About half of the rock is plajrioclase (Aui,, to An.-,(|) which is sliiihtly or not at all zoned, [n addition to the un/oncd ])la;;ioclases there are luimerous crystals with one or two calcic i Aus.-, to Ann,,) zones, or with cores of that composition. Quartz, in anhedral grains with siiarj) extinctioji. avera<>es from 10 to 20 percent of the tonalitc. Hornblende makes up approximately 10 percent of most sections. It forms separate individuals of uni- form composition, or is found as reaction zones around aiii^itc. There is rarely more than 1 to :i percent anyite. ll^perslhene, whicii is limited to the darker phases of the I'ock antl never exceeds o percent, may be partly replaced b.v hornblende. Biotite is the most plentiful fci-roniaiiiiesian mineral, makin<;- up as much as 1.") per- ceiu of most s|)ecimens. Larfre poikilitic flakes are the most connnoH form. Zircon, sphene, apatite, and mafrnet- ite are abundant accessory minerals. Lakeview Mountain Tonalite The Lakeview ilountaiu tonalite is fouiul in an ex- tensive, continuous area in the north-central part of the i|uadram;le and in one body on the western edge. Al- though Hour has been reported to the south or east it is fairly common to the west and northwest. It ap])ears to be youuiicr than the Green Valley tonalite, and Larsen n94S. p. .-)8) fouiul it to be older than the Honsall tonalite. In the area here described, its contacts with rocks other than the Green Valley tonalite are ]ioorly I'xposed, hence no definite age determination could be made. The texture of the Lakeview Mountain toiuilite is phanerocrystalline, hypautomorphic granular with aver- age grain sizes of 2 to o nun. The tonalite is distinguished b.v its very white feldspars and clean-cut ferromagnesian minerals which are commoidy euhedral. The amount of hornblende usuall.v ecpials or exceeds that of biotite; in this respect the Ijakeview Mountain tonalite diifer.s from the other tonalites. Plagioclase is the most abundant min- eral and makes up at least half of the rock. It ranges from An.-is to Auj.,. Orthoclase appears in nearly all sec- tions but seldom exceeds 5 j>ercent. Quartz, with minute, randomly oriented inclusions makes up about one fourth of the rock. Hornblende is mostly automorphic in the l)ri.sm zone and averages 10 percent of the rock. Biotite occurs as large, sonu'times pseudo-hexagonal plates. Epi- dote, formed by saussiu-itization, but also appearing as a primary mineral, is widespi-ead and composes up to 2 or 3 percent of the rock. Sphene, apatite, and zircon are the usual accessories. Residual boulders of ilisiiitegration characterize the Lakeview Mountain tonalite terrain. Such boulders range I'HOTO (i. ■ y^ Residual boulder.s produced by weathering of Lakeview Mountain tnualitf. E.\|ii aiont; Higliwa.v 79 ea.st of Lake Henshaw. Photo by R. M. Stetcart. 14 Califohnia Division' of Mixes IBiill. 177 up to a fow tiMis of foi^t in diamctei- and are sui-roiiiult'd l)y larfre (iiiaiititics of trniss. Structui'os are not i)roiiii- ni'iit ill tlie Ijal\e\ic\v ilouiitain toiialite exeopt aloiio; some contacts wliere a gneissose appearance results from streakin<> of dark inclusions. Joint systems are locally distinct, as in the area west of Ballena. Bonsall Tonalite The Bon.sall tonalite was named hy Hurlbnt (1935), who described its occurrence in the San Luis Rey quad- rangle. The Ferris (|uartz diorite and Val Verde tonalite are considered e(|uivalent to the Bonsall, whieh is i)rob- ably the most extensive rock of the Peninsular Ranjires; however, exposures cover less than 'i percent of the Santa Ysabel ((uadi-anji'le. The dominant rock type is medium- - any process related to assimilation. The Bonsall tonalite is characterized by abundant inclusions that are generally streaked iiarallel to and more numerous near contacts with older rocks. Thus some, and jiossibly most, of the space for injection of this tonalite was gained by stoping. The manner in which older structures are truncated by the Bonsall tonalite rides out emplacement by distension of wall rock. To summarize : evidence for emplacement by forceful injection is generally lacking, although locally this process may have furnished some s])ace. Processes such as melting or re]ilacement were probably not active, considering the sharjuiess of contacts and lack of miner- alogical and chemical correspondence between wall rock and intrusive. Stoping was probably effective in emplacing some of the tonalites. Quaternary Sediments Continental sediments composed of gravel, sand, and silt, older than the alluvium of the present valleys, form irregular remnants surroiuiding the basin occupied by Lake Ilenshaw in the northern part of the quadrangle. Such deposits are also widespread to the northwest in the Temecula area; there they have been termed the Pauba formation (Mann, 1955). The name Pauba forma- tion is not used here, for, although the fanglomerates are similar in most respects, there is no way of corre- lating ages; in fact evidence indicating the age of the Santa Ysabel sediments is exceedingly indirect and in- definite. Within the Santa Ysabel quadrangle the fanglomer- ates have been considerably dissected, and presumably have been removed from large areas. Where the base of the formation is exposed the sediments appear to lie directl.y on a moderately irregular surface of batholithic rocks. No accurate determination of thickness could be made, but continuous exposures ranging in vertical thickness from 50 to 100 feet are common. It is likely that much greater thicknesses are present nearer the center of the Lake Ilen.shaw basin, but this portion is outside the Santa Ysabel quadrangle. Lithology of the formation is that of typical alluvial fans derived from crystalline rocks of granitic oi' inter- mediate composition. The principal rocks present are granodiorite, tonalite, aplite, pegmatite, quartzite, and gneiss. The finer grades consist of fragments of rela- tively fresh plagioclase, orthoclase, mierocline, biotite, hornblende, and (piartz. The feldspars may be exception- ino8i Raxta Ysabei, QuAniiANGLE — Geology 15 ■*^ I'noTO 7. Low hills ill piisccl (if Plcistdcciic (?) iirkdsp faiiKlomPrate. Hui'iia Vista Ci-eck. J'liulo hy K. M. Stfirnit. Warner Uaiii-li almix ally ahimdaiit locall}', especially in seetions adjacent to bodies of Lakeview Mountain tonalite, where the sedi- ment has nearly the same composition as the tonalite. The term arkose would be applicable to this part of the formation (Temecula arkose). Particle sizes ranpe up to 2 feet, although the bulk (if the faiifilomerate is tnade up of cobbles and pebbles with sands and silt interstitial or in lenses. The larger (•lasts are Tnoderately well rounded and become more abundant in an eastward direction. Stratification is generally indistinct or absent but cross lamination, cut-aiul-fill structure, and similar fea- tures are prominent. The source of the faufrlomerate was no doubt the adjacent hijihlands of iorneous and metamorphic com- plex lyiuf,' to the east and northeast. The conditions pre- vailing- at the time of deposition differed from those of today, for removal and deposition apparently were more rapid because of greater relief, greater precipitation, or both. As to age, the fanglomerate can only be said to be post-Cretaceous and pre-Recent alluvium. However, if it is c(iuivalent to the Pauba formation, it is Pleistocene (Mann, 1955). STRUCTURE The major structural features within Santa Ysabel quadrangle are the northwest-trending faults; minor features are the joint .systems, schistosity. and gneissic structure. -— «**" -K^l ".i.,rs.- -;,'>■?>' -S,^*,,. ... .^ i^r:?^ .36.^^• ■ -t^>' ?i^.V--- %. I'lIoKi S. rir'istiicciu' I '.' ) ai'kdse c.Niioscd in iciad out ndrthcast of I>ake Hensliaw. If! California Division of Mines [Bull. 177 EXPLANATION Qs- Sediments Kb Bonsoll tonolite Lokeview Mountoin I ona I il e Kg Green Volley tonolite Son Morcos qobbro JS Stonewall quorti diorite Mined rocks (Stonewall end schist) ■fij A 5 000'-, Julian schist 4 5/\ Contoct (doshed if '// grodational or oppfoxim Strike and dip of beds Strike of vertical beds S'rike ond dip of pri mory foliation Sfrike of vertical primary foliation \\ Troce of flow lines showing general sfructurol grain Strike ond dip ot loints Strike of vertical joints 4 Trace of joints Qs r^'^'"°''^ '""^ -.^rr'»>— ^-^ San Fell pe fault. (ofiTose) A' m Ir. ■■■■•■ •■•■•■ Son felipe foulf FuiUKlc li. Sti'uctiire mnii and sections, Santa Ysabcl (|iKulraiiKle. 19581 Santa Yrabel Quadrangle — Geolo(iv 17 Photo 0. Trace of tlic Klsiijini' tnull zone follows foot of mountain along south shore of Lake Henshaw. I'alomar Mountains in lanse at far right. Carrizo Creel; flows down valley (also along fault zone) in left foreKround. San Luis Key River flows westward from Lake Ilenshaw through gap in center Itaclvgronnd. f'hoto In/ J'. M. Stcirnii. Julian Schist 111 the .Tiiliaii scliist, attitude of sehistosity — also gen- erally that of tlie beddiiio: — is the most obvious stnietui-e in the field. The dips are for the most part essentially vertieal and the strikes are eommonlj' parallel to eoiitaets and to long dimensions of the sehist bodies. The bulk of the formation follows the regional northwest strike, although exeeptions to this are eommon, particularly in the south part of the area where the sehist wrajis around a large gabbro body. igneous Rock Structures No attemjit was made to map in detail all of the various primary igneous structures. However, even a .sketchy consideration of some of the more obvions ele- ments is enlightening. Several igneous formati(uis ex- hibit distinct schlieren. streaked inclusions, and segregations. "Where these are absent the rocks often show a parallelism of tabidar or flak>- minerals. Ivocall.w joint systems arc iirominent enough to bi' easily ma])]ii'd and included in the structfiral picture. Stonewall (Jiiniiz Duirtic. The Stonewall quartz dio- rite exhibits - arrangement of schlieren or inclusions of schist. The latter are widespreatl and range from hand-siiecimen size to streaks large enough to map. Locally the rocks are gneissose to schistose. There is considerably more detail than can be shown on the accompanying map. Attitudes rarely can be determined accurately, but near- vertical dips are the rule. Strikes parallel those of the schist but may be crossed by batholithic rocks. Lake view Mouniuin Tonalite. The Lakeview ^Moiui- tain tonalite is massive over wide areas but shows a dis- tinct systematic structure in the small area west of Ballena. Here streaked dark inclusions parallel nearly all contacts. Platy inclusions are essentially vertical Vertical joint plaru's are both parallel to and normal to some contacts. Boiisall Toualilc. Characteristically the Bonsall tonal- ite contains abundant inclusions most of which are streaked or platy parallel to contacts with older rocks. In the Santa Ysabel quadrangle, inclusions are not so abundant, although some idea of the strtictnre can be gotten from them. All other igneous rocks in the area are massive or possess oidy local or unsystematic structures. Faults The evidence for faulting is largely indirect in Santa Ysabel ((uadrangle. because is ways. Some may be situated in easily weathered and eroded rock surrounded by more resistant rock types. Others may I'epresent i-emnants ol' an old erosion surface. Although there may be little 01- no correspondence in elevations, this can be explained b,v faulting. All the major drainage lines are characti'rized by nu- merous deviations from the ideal concave uj)ward profile. iS'ick points, although present, are less common in Santa Y.sabel (juadrangle than elsewhere in the Peninsular Ranges, because of the lack of contrast in I'esistance of the formations. Some of the outstanding irregularities in long |)rofiles have resulted from faulting. Thus Santa Ysabel Creek ajid several unnamed streams begin with relatively low- gradients in the Volcan area but soon plunge down the steep Elsinore fault scarps to the west, then resume low gradients as they traverse the lowlands. GROUNDWATER Groundwater is one of the most impor-tant natural resources of Santa Ysabel (|uadrangle, and the present trend is Toward even greatei- iinpoi-tance. (ii'oundwater resources of parts of the quadrangle have alreadv been described by Ellis and Lee (1919). l^V;H Jc;.sf Vullcii i Laki fl< iishaw) . San Jose Valley has an area of about '.]'2 scpiare miles, much of which lies within the Santa Ysabel ipiadrangle. It is roughly rectangidar in plan and is bounded on all sides by granitic mountains. Depending upon the precipitation of the current year and other factors, as nuich as half of the basin is covered with waters of the artificial Lake Ilenshaw. The exiiosed portion is underlain by Recent alhiviuni aiul Pleistocene gravels to a depth of 200 feet or mori'. These sediments have slight basinward dips, especially those in the northeastern sector. Because much of the drainage lies in this portion, the conditions are favorable for recharging the underground reservoii- of the valley. The water table has always been shallow, geiierallv 10 f(>et or less. Numerous northwest-striking I^^Z «itV*"'V I'lioio 11. Elsinore fault zone in Bniiiicr ami KodriKucz C.-in.vons as seen finin .luliaii Ricl;;f. Uaiicliitd mine is in flat of HoilriKue/. Can.viin Ijeliiw (Inniite McmrHaiii al rit:lil. San Felipe \'alle,\ e.xtenils mirtliwaiil in left einitei'. I'hotn hii II. 1/. Slrirtirl. •_'() Califorxia Division of Mines [Bull. i: faults have brought tlie water table to the surface in many plaees. Warner's Hot Spriufis was i)ro(lueed in this way. In 19.')! the owners of Lake Ilenshaw drilled a number (if wells in the upper part of the basin; the water was pumped intd the lake to augment the aeeunnilation from surface nuiotf. Sail Ysidro and Buena Vista Creeks are tributaries to the main San Jose Valley. Groundwater from San Ysidro Mountain and ^Montezuma Valley passes down this drainat;e and is locally broujiht to the surface by faultintr. There is every indication that fairly productive water wells could be drilled in this area. Montezuma Vallcn. Montezuma Valley is underlain by a thin layer of alluvium coverinp' an irregular bed- rock surface. It is bounded on the north by the San Ysidro Mountains which, rising 2,()()() feet above the valley, make the only important contribution to the groundwater of the valley. Due to the bedrock con- figuration, characterized by the trough of San Ysidro Creek along the north side of the valley, the runoff from San Ysidro Mountains does not reach most of the valley in ajipreciable (piantities. Inflow to the water table is very meager exce)>t in the northern part of the valley. Faults, which are probably the contin\iation of those producing the springs at "Warners and vicinity, pass through Montezuma Valley bringing water to the sur- face at a few places. Several springs along the foot of San Ysidro Mountain probably result from faulting. Bedrock in Montezuma Valley is probably largely Bonsall toiialitc which is a favorable formation for the drilling of laterals. Such wells are most likely to be successful. Santa Y.saljcl* Appreciable ipiantities of ground- water are limited in Santa Ysal)el valley to the area adjacent to Santa Ysabel Creek. There the alluvium may be as much as 100 feet in thickness. The How of surface water, which fluctuates widely, is the chief factor gov- erning the yield from this alluvium. Elsewhere in the valley bedrock is shallow, its cover is largely relatively imiiervious residual material, and conditions are gener- ally unfavorable for productive wells. A minor fault along the north end of the vallc.x- i)ro(luccs a row of small si)rings. San Felipe Vallaj. San Felijie Valley has an area of approximately 20 .square miles. It appears to have been formed structurally as a roughly triangular graben bounded on the east by the San Felipe fault. The high No name indicated on topograpliic map ; this is tlie valley occupied by Santa Ysabel Creek and the town of Santa Ysabel. ai-ca to till' west and southwest, that is, Volcan Moun- tain, .Julian, and Julian Ridge, constitutes the chief source of surface and subsurface water for the valley. Banner Creek, entering from the southwest, varies in volume but is perennial and seldom flows less than one second-foot. San F'elipe Creek, flowing southward from the north end of the valley, is intermittent. Extensive alluvial fans, dipjiing steeply in their ujiper jiortions, emerge from canyons on Volcan Mountain. As the an- nual precipitation in these mountains averages more than 30 inches, this is an ideal situation for recharging the groundwater reservoir. The water table is shallow throughout most of the valley. This has been noted in the few small wells ami is also indicated by vegetation such as willows, cotton- woods, and swamjiy grasslands. GEOLOGIC HISTORY The earliest event recfirded in the geologic history of Santa Ysabel quailrangle is the deposition during the Triassic (?) of a series of sediments, principally ter- rigenous, but containing some volcanics, which are now rejireseiited by the metamorphic rocks. The sediments were metamorphosed aiul complexly intruded by the Stonewall ((iiartz tliorite and related rocks. The date of this intrusion is tentatively placed in the Jurassic. The whole comjilex was then sub.iected to a period of regional metamorphism of intensity ap])roximately equivalent to that of the me.sozone. In the Upper Cretaceous, batholithic rocks were em- placed : first gabbro, then Green Valley toualite. Lake- view Mountain toualite, and Bon.sall toualite, in that order. In some (lortions of the Peninsular Ranges out- side the Santa Ysabel (piadrangle, batholithic invasion continued, emplacing several granodiorites and t(uartz monzoiiites. Although the geologic record from Cretaceous to Pleistocene is missing in Santa Ysabel (piadrangle, sedi- ments in the nearby Ramona and El Cajon quadrangles indicate almost complete deroofing of the batholith by upper Eoi'cne time. Coarse Oligocene ( ?) breccias in the adjacent Borrego (piadraiigle suggest that the Santa Ysabel area was elevated at that time. During the Pleistocene ( ? ) , fanglomerates accumu- lated in parts of the Peninsular Ranges, the particular position and thickness being controlled by faulting which created basins. Faulting has continued to the present and has been the dominant factor in producing the existing topography. This was accomplislied directly by the relative elevating of some sections and depressing of others, and indirectly by the dis.section made jiossible by rejuvenation of streams. MINES AND MINERAL RESOURCES OF SANTA YSABEL QUADRANGLE SAN DIEGO COUNTY, CALIFORNIA I:y liu:HAi:u .M. Stkwakt " OUTLINE OF REPORT The nortlicnuiiost district within the qnadranfrle is ^9^ the Rice or Montezuma district on the southern sh)pes . .7i of the Sail Ysiilro Mountains north of Montezuma Val- .,| le\-. .liihaii sc-hist, Stonewall (|uartz dionte, and mixed \'i' "-n "-1 rocks — a complex of Julian schist and Stonewall (juartz ' .' _ 2.-, dioite — undei-lie the area; but most of the frold-bearinfr ,„ ' '" .,- (luartz veins are enclosed in the metamorphic rocks. The ... ,, .-,-, veins are di.scordant with the enclo.sin<;' rocks ami have ,.,.,,., .,-, a general strike of X. bo^ F.. and a dip ot /0° NW. I.i^r 1)1 mines iiiid miiK'nil (loposits __ — i ., , ■ , • i , . , i Although several properties have been prospected and Illustrations exjilored, oiilv oiic has been extensively developed. Work- I'iKiire 1. ]>i:i);i;imniatu- skt-teh ..f a iiiiait/. roll striietiirc in iii^s oil this, the Montezuma mine, reached a maximum schist 23 de])th of 2.'i() feet. The amount of production, althoufrli I'll.. I'. I. <;i.i(lcn Chariot mine in Chariot Can.von 2:^ Hot detpmiiiied, was probably small. A mill oil the prop- •J. Ij.'uuhito mine in Koilrifjura Can.von flat 2'J c-ty was destroyed by fire ill 1913. :{. Traoi- of worlible. most imjiortant mineral resource in the Santa Ysabel . t , ■ ^ quadranole. The oreatest amount of fiold was produced "'' •/'''"'" Z^.'-^"'"''- The Julian distr.c encompasses here durino- the period 1870-80. Marble, chietlv as di- L-hieHy tlio.se mines -rouped within a relatively narrow mension .stone, has been produ<-ed but the deposits have -;>-'P «bout < miles lon^ that extends northwestward lono- been idle *^'''"" ^'"^ '^'•'""t.^' <>f the Golden Chariot mine in Chariot Despite the presence of nickel ore in the Julian dis- t'«",y'"> V-'^' I>«""!^'- «'»' thence curves somewhat more trict. the proved reserves are small and no commercial to the west to a point about a mile northwest ot Julian, production has been made. Deposits of lithium minerals ■}, t^-.^ '">'"'-• 'i.'f "' }\^ Julian district, are sparsely ami of wollastonite are known within the quadranple distnbnte.l outside ot this strip. These include -old de- but have not been of commercial si^rnificance. An area I'osits that lie eas . southeast, and south of Banner, and in the northeastern part of the .luadranolc is beiiio inckcliterons pyrrhotite deposits southeast of Julian. The .•xpl.ircl tor de,,osits of tunosten ore, but other miiiino St.mewall mine south of C uyamaca Lake in the C uya- a.-tivitv is jreneiallv limited to the performance of re- '"!'«' •^'^"!' '""■•<• ^^'T''} H- f ,'" '. f" ^l""' quired" assessment work. '■•'"f- >"." '^ ^"•">' ''^ the Santa \ sabel quadranole The approximate boundary line or the Julian district was MINERAL DEPOSITS defined ill 1881 (Hanks 1886, pp. 83-84) ; the greatest Gold part "f the district lies within the quadrangle. The most ,, , . . -.1 ■ .1 o . A- 1 1 1 i-,-cc)it description of the peologv of the mineral dejwsits .\ list 111 the iiiinino- within the S;iiita Vsabel quad- .. .' . ,. . , -r> n cinQi . •}^)^ •}-<> , , ^ , ^ ,. ,, , -^ . ,,, 1 nt the district is that bv Donnellv (1934, pp. 331-.5K), lano (■ has centered upon the ooUl deposits. Altlionpli , ,, i i- .i t n' • r '„„,;„„ • k... a ,,..„.. ,7 , , ' „ r ■.. ■ 1 pl. 4i; iiiiich ot the lollowino- (liscu.ssion is based upon ccild has been recovered from deposits in several areas j • . . .^ within the quadranole. the o-reatcst concentration of "^ lepoi • , , ., I , ■ 1- ..• • • ..u I r tj i;.t„;,+ fii^ Lo( c oi, ( (Cpcisits were < iscovere( subsequent to the oold iiiineralizatimi IS 111 the Juliaii-Baniier district, ine ■ .. / i •. i r. i /. i 1 111 u K .. 1 «„„,i ..o „i;.,;„„- (qici;itiiin nt placer tleposits alonl\ TJ1 I- , 1 ♦! 11 ,„;.,;„ , i; t,.; t.- t,.„ot;,.,,. fi,,. ininini; i isirict was tormallv or-ranized on hebrnary ];>. 130. J31 I listed three ooid miiiino' districts, treatiiio' tlic -.in". in.-.,- ^o , ..iV • liaiiner ami Julian areas as .separate .listricts. ami nam- ^ ^'^'- ^""1 ^^''-^ described ( Hanks, h.sb. p. hi ) as B.-m- ino the Bice district as the third. Merrill (191(5. pp. nnig <,ne thousand yards west of Ilarrolds Store and 648-649, 6O3-660) named an.l separatelv discussed the '■'•';'""^- ""'.-^l' ^.^ •"'•'■^ «"< south five miles and four Rice (Montezuma) an.l the (irapevine .listricts. but >'''''''. '''1 '," "i '' /. ^■^''^'''\Pf}''l ^ccn-der. ^ 1 .1 r> 1 T 1- r «..; t The first ode claims, t he Cieorjre \\ ashmprton and Van treated the Banner and Julian areas as (uie district. ,,; , . i t-, i oo ^o-,^ t » ^ ■ .i T 1 .1 i> 1 T r . ... „ o,. „o 1, ^^ ert. were located on Februarv 22. IhfO. Interest in the Inasmuch as the Banner and Julian areas are near each ' '.■ . . • , ,. , . . . , ,, , , ■ 1 •» ,1 t , .., *; .,11,. .. ,i..t,..i district was keen, and within b months after these initial other and coiitani deposits that are uencticallv related. . , , . , , , t;i i -.i n r * • » , 11 • 1 1 I 11 1 1 isc(i\-eries .)4 <• ;imis hai been filed with the district lliev are o-enerallv considered as one — cdiiimonlv called the Julian district. recorder. ,,, . . ,. ,. In Auo-iist 18/0 a o()|,|.bcanii.o- vein was iliscovered in 'mnu-!"%rpumTM\on^^^^^^^^^ iV.'li'sT. "' "'"'"■'' •'"^'"""'■'■'■" "'"'■ Chariot Canyon (or San F,-lipe Canyon as it was then (21 ) 22 California Division of Mines I Bull. 177 s;v» .'.>;-■■■ ■,;-i<^ *i ^^•' I'TIOTO 1. Goklen Chiiriot mine in Clnu-inl Canyon. known) and named the Redman after one of it.s dis- coverers. As Redman had marked his claim witli a small American fla^', the name Banner was piveii to the small connuunity nearby. Many other claims were soon located on the slojies of Chariot and Banner Canyons. Two of the more pi'oduc- tive mines were amonu' the last to be discovered — the Helvetia late in 1870, and the Golden Chariot in Febru- arv 1871. Tlie period of f>reatest activity in the Julian district was from 1870 to 1880, and the annual gold production reached a peak value of about .fi500.000 in 1874. Many of tlie mines were shut down by 1875. and the famous Golden Chariot had shut down by 1876. In 1888. the discovery of the Gold Kiiip: and Gold Queen mines, about 4 miles soutlieast of Julian, renewed the ho])es of prospectors, and activity was resumed at many mines. In 1895, the Elevada and Rancliito mines ^■"^y^p-'- '«». . ->,.., ■tt^^- ^ .j^*»'vT- . ^^i^^^^ite Photo 2. Kanchito mine in Rodriguez Can.von fiat. There i.s a five-stamp mill between dumps. ior)8i Santa VsAnr.i. Qt-adranoi.e — Mines and Minkrai. Hesot'rces 2.'j wore (liscoven'd ; in ISiKi llip Owens mine was rco|iPiu'(l foi- tlic second time. These operations were short lixi-d. and little jrold lias been prodnced from the district durinfr this century. Considerable exi>ioration was undertaken at the (Jolden Chariot mine, stai-tin^: in l^i'I'-i. and aelivily was n-newed at the Ready Heliet' and nearby claims during: the same period. From l!t2:} to VXi'.i the total value of "rold pro- duced was .slightly less than $4;i,()U(). I'lacer operations accounted for about 10 percent of this total. The value of the total estimated production from the district is between $2.r)()().()()(l and A;i()()0.()(l(l. Virtually all of the recent activity has been in the performance of assess- ment work, and production has been ne' Donnelly i l!i:U. j). :{.").j i on the liasis of shape as h'nses. lenticular veins, and rolls. Lenses are abundant but individually quite small. commonly bein;roun(l. Fii;rRK 1. DiaKrammatic .sketch of a quartz roll structure in sclli^t. Xol to .scale. HnnKinK wall s..i <(i"" n \^npif,! t,,,,,, Doiiiirlh/ lO.ii, p. S.'ji;. vein, exphjred for 800 feet by workings in the North Hubbard mine and for 600 feet by Read.v Relief work- ino:s. is at least 1400 feet long: (Tucker 1925. p. 347; \'Xi9. pp. 26-27). However, the.se workinsrs may have explored parallel, closely arl.iacent veins of lesser length. .Most veins are iirobably much shorter. The veins com- monly are composed of bands of quartz separated by thin films or layers of scliist a fraction of an inch in thickness. In general the veins that lie northwest of the Ready Relief mine are en echelon in plan. Associated with the lenticular veins are the quartz bodies with roll structures; these bodies are called "rolls" by Donnelly. In cross section, a t.vpical roll structure shows a tabular body of cpiartz. concordant down dip with the enclosing schist, merging into a short trough which transects the .schist, changing again to a tabular body concordant for a short distance up dip: then conies a .short transecting saddle followed by a tabular body extending farther down dip. A single body may have several such individual rolls down dip. The conformable portions ma.v be thicker at the troughs or .saddles, and the combined thicknesses of several closely ad.jacent limbs may be as great as 20 feet. One roll was followed for a strike distance of 500 feet, but most rolls range in length from 20 to 100 feet. Most roll structures extend down dip only several tens of feet; a few extend more than 100 feet. The axes of most rolls l>lunge to the northwest at a low angle, usually le.ss than 25 degrees. Like the lenticular veins, the bodies forming rolls commonly consist of layers of quartz separated by thin schist seams. Roll structures were probably pro- duced b.v deposition of quartz in fractures that partl.v follow and partl.v tran.sect the schistosit.v rather than b.v post-mineral folding of tabular fpiartz veins. 24 California Division of Mines [Bull. 1' Lenses, leiitieiilar veins, and rolls oeeur near eaeh other throughout the sehist belt in the Julian district. However, a single type may be more completely devel- oped in certain mines — rolls in the area near Banner from the Warlock to the South Hubbard mines, and lenticular veins in the Golden Chariot, Helvetia, and Owens mines. Rolls are known to have merfjed into len- ticular veins alonfj the strike. Lenses are present in all mine areas. All three types of {(uartz bodies are believed to have formed at the same time. All types of deposits trend northwestward, ranginjj- in strike from N. 20° W. near the Golden Chariot mine to N. 60° W. near Julian. The dips are generally uortli- east except where slumping of the schi.st and enclosed veins on steep slopes has resulted in dips to the south- west. The principal gangue mineral is (piartz, both massive and banded ; the banded quartz is nearly always highly strained. Coarse-grained biotite is associated with much of the quartz. Tourmaline is present in very minor pro- portions in some veins and probably indicates a high- temperature origin. The ore minerals consist of free gold and some gold telluride (probably petzite), associated with arsenopyrite, pj-rrhotite, and pyrite; tiic suljihides are auriferous. Records indicate that most ore shoots were discon- tinuous and small, and that abrupt changes in grade of ore were encountered. Probably the most extensive ore shoot mined was that in the Owens mine where ore was stoped along 400 feet of vein through a vertical range of 800 feet. The principal ore shoot in the Helvetia mine was 100 feet long and had a di]! length of ITH) feet ; a shoot mined in the Golden Chariot was (i.") feet long and 185 feet in dip length. Stope lengths of 125 and 150 feet are reported in descriptions of the Eagle mine, but no indication of vertical extent i.s given. Two ore shoots, each having a maximum dimension of 45 feet, are reported in descrip- tions of the Redman. The size of most shoots in the district was probabl.y of that order or smaller. Li most of the mines the ore shoots pitch to the northwest. Donnelly has estimated that the average tenor of the ore from the principal mines was $50 per ton (2| ounces of gold per ton), but a wide range of values has been reported. Some material from the Eagle mine yielded as little as $2.75 per ton when milled (Hanks 1886, p. 85). Mining such rock was probably not economic. Other deposits however, contained high-gi'ade ore; 100 tons of ore from the Golden Chariot yielded $32,000 ( Hanks 1886, p. 86 ) , and 920 tons of ore from the Owens yielded more than $42,000 (Hanks 1886, p. 87). Small amounts of ore valued as high as $500 per ton were mined from several properties. However, the relative thiiniess of the deposits and the small size of most ore shoots made profitable mining operations difficult in spite of the grade of the ore. ilost of the mine workings have been relatively shallow ; the 350-foot shaft on the Golden Chariot vein, and the long cross cut adits extending under the Warlock and the Kentuck groups probably reach the deepest points below surface outcrops of any workings in the district. Less free gold and more aurifer- ous sul]iliides have been encountered in the deeper work- ings and this trend will probablv continue at greater depth iDoinielly 1934, p. 369). > -'Mm-W '^^k-:^- PiKVK) 4. VcvniR'n marble qu.irry im ."inuth .slope of San Y.sidro .Mountains. .\lai'l)l(' iji contact with sclii.st in riylit center of pictiu'e. Considering the nature of the ore and the apparent vertical range of deposition (a difference of about 1,800 feet in altitude exists between the highest and lowest surface points in the mineralized belt) the deposits are clas.sed as hyi)othermal and are thought to be genetically related to the Stonewall ipiartz tliorite but later in age. Marble Two of several relatively small lenses of marble, en- closed in schist roof pendants bounded by Stonewall quartz diorite, Lakeview Mountain tonalite, and mixed rocks, have been i|uarried to provide dimension stone and, more recently, rooting grannies. The white to gray, slightly banded, c(iarsel\' crystalline marble is a nearly pure er Mininji Company of San Diciro (Merrill lt)16, pp. 66(5-667). Most of the underfrround workin<.'s were tlriven by tliis company; more recent exploration has consisted larfrely of diamond drillinfr. Other deposits, havinpr similar but smaller fros.san outcrops, have been prospected by shallow pits. Dnrinjr the late inSOs a les.see drilled two diamond drill holes to a depth of about 500 feet on other sros-san outcrops, but neither disclo.sed ore: one hole was a few hundred yai'ds north- west of the Frida.v shaft and the other was about one mile we.st. The massive sulfide ore body of the Friday deposit was once considered to have formed by syncrenetic majr- matic concentration (Hud.son 1922. pp. 227-228. 238- 241 '. A more recent study (Crea.sey 1946 "i cites evidence supporting a replacement orif^rin. Snlfide-rich. silica- poor solutions are thou