3 STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES GEOLOGY OF A PORTION OF THE ELSINORE FAULT ZONE CALIFORNIA SPECIAL REPORT 43 -^^STtY OF CALIFOKN.A DAVIS ; 2 i iS55 DIVISION OF MINES FERRY BUILDING, SAN FRANCISCO SPECIAL REPORTS ISSUED BY THE DIVISION OF MINES l-A. IB. 2. 3. 4. 6. 7-A. 7-B. 8. 9. 10-A. 10-B. 10-0. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. Sierra Blanca limestone in Santa Barbara County, California, by George W. Walker. 1950. 5 pp., 1 pi. Price 25*. The Calera limestone, San Mateo and Santa Clara Counties, California, by George W. Walker. 1950. 8 pp., 1 pi., 6 figs. Price 25 *. Geology of part of the Delta-Mendota Canal near Tracy, Cali- fornia, by Parry Reiche. 1950. 12 pp., 5 figs. Price 25*. Commercial "black granite" of San Diego County, California, by Richard A. Hoppin and L. A. Norman, Jr. 1950. 19 pp., 18 figs. Price 25*. Geology of the San Dieguito pyrophyllite area, San Diego County, California, by Richard H. Jahns and John F. Lance. 1950. 32 pp., 2 pis., 21 figs. Price 50*. Geology of the Jurupa Mountains, San Bernardino and River- side Counties, California, by Edward M. MacKevett. 1951. 14 pp., 1 pi., 14 figs. Price 25*. Geology of Bitterwater Creek area, Kern County, California, by Henry H. Heikkila and George M. MacLeod. 1951. 21 pp., 2 pis., 15 figs. Price 35*. Gem- and lithium-bearing pegmatites of the Pala district, San Diego County, California, by Richard H. Jahns and Lauren A. Wright. 1951. 72 pp., 13 pis., 35 figs. Price $2.50. Economic geology of the Rincon pegmatites, San Diego County, California, by John B. Hanley. 1951. 24 pp., 1 pi., 5 figs. Price 35*. Talc deposits of steatite grade, Inyo County, California, by Ben M. Page. 1951. 35 pp., 11 pis., 25 figs. Price 85*. Type Moreno formation and overlying Eocene strata on the west side of the San Joaquin Valley, Fresno and Merced Counties, California, by Max B. Payne. 1951. 29 pp., 5 pis., 11 figs. Price 60*. Nephrite jade and associated rocks of the Cape San Martin region. Monterey County, California, by Richard A. Crippen, Jr., 2d printing. 1951. 14 pp., 14 figs. Price 25*. Nephrite in Marin County, California, by Charles W. Chester- man. 1951. 11 pp., 16 figs. Price 25*. Jadeite of San Benito County, California, by H. S. Yoder and C. W. Chesterman. 1951. 8 pp., 6 figs. Price 25*. Guide to the geology of Pfeiffer-Big Sur State Park, Monte- rey County, California, by Gordon B. Oakeshott. 1951. 16 pp., 1 pi., 28 figs. Price 25*. Hydraulic filling in metal mines, by William E. Lightfoot. 1951. 28 pp., 15 figs. Price 50*. Geology of the saline deposits of Bristol Dry Lake, San Ber- nardino County, California, by Hoyt S. Gale. 1951. 24 pp., 1 pi., 2 figs. Price 35*. Geology of the massive sulfide deposits at Iron Mountain, Shasta County, California, by A. R. Kinkel, Jr. and J. P. Albers. 1951. 19 pp., 6 pis., 6 figs. Price 75*. Photogeologic interpretation using photogrammetric dip calcu- lations, by D. H. Elliott. 1952. 21 pp., 9 figs. Price 50*. Geology of the Shasta King mine, Shasta County, California, by A. R. Kinkel, Jr. and Wayne E. Hall. 1951. 11 pp., 3 plB., 4 figs. Price 50*. Suggestions for exploration at New Almaden quicksilver mine, California, by Edgar H. Bailey. 1952. 4 pp., 1 pi. Price 25*. Geology of the Whittier-La Habra area, Los Angeles County, California, by Charles J. Kundert. 1952. 22 pp., 3 pis., 19 figs. Price 50*. Geology and ceramic properties of the lone formation, Buena Vista area, Amador County, California, by Joseph A. Pask and Mort D. Turner. 1952. 39 pp., 4 pis., 24 figs. Price 75*. Geology of the Superior talc area, Death Valley, California, by Lauren A. Wright. 1952. 22 pp., 1 pi., 15 figs. Price 50*. 21. Geology of Burruel Ridge, northwestern Santa Ana Moun tains, California, by James F. Richmond. 1952. 1 pi., 11 figt Price 50*. 22. Geology of Las Trampas Ridge, Berkeley Hills, California by Cornelius K. Ham. 1952. 26 pp., 2 pis., 20 figs. Price 75* 23. Exploratory wells drilled outside of oil and gas fields in Cali fornia to December 31, 1950, by Gordon B. Oakeshott, Lewi T. Braun, Charles W. Jennings, and Ruth Wells. 1952. 77 pp 1 pi., map. Price, map and report, $1.25 ; map alone, $1.00. 24. Geology of the Lebec quadrangle, California, by John C Crowell. 1952. 23 pp., 2 pis., 10 figs. Price 75*. 25. Rocks and structure of the Quartz Spring area, northen Panamint Range, California, by James F. McAllister. 1952 38 pp., 3 pis., 13 figs. Price 75*. 26. Geology of the southern Ridge Basin, Los Angeles Countjl California, by Peter Dehlinger. 1952. 11 pp., 1 pi., 7 figs Price 50*. 27. Alkali-aggregate reaction in California concrete aggregates by Richard Merriam. 1953. 10 pp., 12 figs. Price 35*. 28. Geology of the Mammoth mine, Shasta County, California by A. R. Kinkel, Jr. and Wayne E. Hall. 1952. 15 pp., 9 pis 5 figs. Price 75*. 29. Geology and ore deposits of the Afterthought mine, Shast County, California, by John P. Albers. 1953. 18 pp., 6 pis 9 figs. Price 75*. 30. Geology of the southern part of the Quail quadrangle, Oali fornia, by Charles W. Jennings. 1953. 18 pp., 2 pis., 16 fig* Price 75*. 31. Geology of the Johnston Grade area, San Bernardino County California, by Robert Barton Guillou. 1953. 18 pp., 1 pi., 1' figs. Price 75*. 32. Geological investigations of strontium deposits in souther California, by Cordell Durrell. 1953. 48 pp., 9 pis., 12 fig* Price $1.25. 33. Geology of the Griffith Park area, Los Angeles County, Cali fornia, by George J. Neuerberg. 1953. 29 pp., 1 pi., 15 figs Price 50*. 34. Geology of the Santa Rosa lead mine, Inyo County, California by Edward M. Mackevett. 1953. 9 pp., 2 pis., 3 figs. Prio 50*. 35. Tungsten deposits of Madera, Fresno, and Tulare Counties California, by Konrad B. Krauskopf. 1953. 83 pp., 4 pis., 5 figs. Price $1.25. 36. Geology of the Palen Mountains gypsum deposit, Riversid County, California, by Richard A. Hoppin. 1954. 25 pp 1 pi., 32 figs., frontis. Price 75*. 37. Rosamond uranium prospect, Kern County, California, b; George W. Walker 1953. 8 pp., 5 figs. Price 25*. 38. Geology of the Silver Lake talc deposits, San Bernardin County, California, by Lauren A. Wright. 1954. 30 pp 4 pis., 18 figs. Price $1.00. 39. Barite deposits near Barstow, San Bernardino County, Cali fornia, by Cordell Durrell. 1954. 8 pp., 4 pis., 1 fig Price 50*\ 40. Geology and mineral deposits of the Calaveritas quadrangle Calaveras County, California, by Lorin D. Clark. 1954. pp., 2 pis., 6 figs. Price $1.75. 41. Geology and mineral deposits of the Angel Camp and Sonon quadrangles, Calaveras and Tuolumne Counties, California by John H. Eric, Arvid A. Stromquist, and C. Melvin Swin ney. 1955. 55 pp., 4 pis., 21 figs. Price $3.75. 42. Geology of mineral deposits in the Ubehebe Peak quadrangle Inyo County, California, by James F. McAllister. 1955. 6J pp., 3 pis., 26 figs. Price $2.00. 43. Geology of a portion of the Elsinore fault zone, California by John F. Mann, Jr. 1955. 22 pp., 2 pis., 5 figs. Price 75* STATE OF CALIFORNIA GOODWIN I. KNIGHT. Governor DEPARTMENT OF NATURAL RESOURCES DeWITT NELSON. Director DIVISION OF MINES FERRY BUILDING, SAN FRANCISCO 11 OLAF P. JENKINS. Chief AN FRANCISCO SPECIAL REPORT 43 OCTOBER 1955 GEOLOGY OF A PORTION OF THE ELSINORE FAULT ZONE CALIFORNIA By JOHN F. MANN, JR. Price 75^ GEOLOGY OF A PORTION OF THE ELSINORE FAULT ZONE, CALIFORNIA By John F. Mann, Jr.* OUTLINE OF REPORT Pliocene or very early in the Pleistocene the Santa Rosa basalts Pap-f were extruded on this surface. Shortly after these extrusions the tbstract 3 fl rs t important movements along the Elsinore fault zone occurred. ntroduction 3 The Temecula arkose was deposited in the early Pleistocene by 'hysiography 4 streams flowing southwest from the vicinity of San Jacinto Moun- itratigraphy 7 ta j n _ Basement rocks 7 j n the middle Pleistocene another broad alluvial surface was Tertiary sediments 9 broken by great vertical movements of the Pasadenan orogeny; Santa Rosa basalt 9 t ne Elsinore-Temecula trough was formed. Great exhumation of Temecula arkose 10 bedrock surfaces accompanied this uplift, and its progress is Pauba formation _ 13 marked by several broad erosion surfaces and numerous terraces. Dripping Springs formation 14 The Santa Ana River developed a subsequent tributary down the Nigger Canyon volcanics 15 Elsinore-Temecula trough and captured the San Jacinto and Temec- Terrace gravels and Recent alluvium 15 u l a Ri ver s. The Pauba formation was deposited. Then a stream Structure 16 eroding headward at Temecula Canyon captured the drainage of Major structural features 16 the Temecula region. About the same time the basin of Lake Nature and magnitude of displacements 17 Elsinore was downfaulted. Closely following this faulting the Age of the faulting 18 Dripping Springs fanglomerates were deposited. In very late dineral resources 18 Pleistocene time the Nigger Canyon volcanic rocks were erupted Soil 18 during two periods of volcanism separated by several hundred feet Water 18 f erosion. Minor faulting has continued through the late Pleisto- Hot Springs 19 cene an( j Recent. Sand and gravel 19 Principal mineral resources of the area are soils and water. Rock 19 Other mineral commodities which have been produced are sand and Clay U gravel, rock, and clay; diatomite is known to occur. Structural Diatomite 19 control of ground water movements has been important. Springs are Oil and gas . D common along faults. The Wildomar fault is an important barrier Late Cenozoic geologic history 19 to ground-water movement and has created areas of artesian flow References 22 ; n p auDa an( j Santa Gertrudis Valleys and also about a mile north ..... of Temecula. Illustrations Page INTRODUCTION Plate 1. Geologic map of the Temecula region In pocket . . . 2. Structure sections of the Temecula region In pocket The area mapped for this report is in western River- Figure 1. index map showing the location of the side and northern San Diego Counties, in southwestern Temecula region 4 California (fig. 1). It lies about 25 miles from the coast, 2. Geomorphic provinces of southern California 5 q - -i f t Angles and 70 miles from San Dipp-o 3. Physiographic units of the Temecula region 6 %> mUes Irom ^ s Angeles, ana i. • i.- the Temecula and Aguanga basins, occupying downfaulted blocks of features of the Peninsular Ranges physiographic prov- a Mesozoic basement complex on which late Cenozoic continental ince of Reed ( 1933 ) . sediments have been preserved. The Temecula region consists of two basins of rela- Basement rocks of Paleozoic and Triassic metasediments and tiyely low re]ief surr0U nded by basement highlands. In Jurassic metavolcanic rocks nave been intruded by Cretaceous plu- .•■ ■£. ■ .-i •■• » i , , rn r\ tonic rocks. Upon a mature erosional surface of the basement com- the basms the rellef rarel y amounts to as much as 500 plex were deposited Paleocene (?) arkosic gravels. Small patches of feet. The lowest elevation (less than 1000 feet above these are preserved under olivine basalt flows of Pliocene (?) age. sea level) OCCUrs at the east end of Temecula Canyon, Preserved within the basins and in places outside of the basins is through which passes all the drainage of both basins. On the Temecula formation, consisting of more than 600 feet of white . nvi- ■»*■ j. • ax. ,i , j ,. ,v to buff arkoses, brown silts, silicified algal marls, and white tuff. A S ua Tlbia Mountain, the northwestern end of the mas- Lying above the Temecula formation with marked unconformity is sive Palomar horst, the elevation is more than 4700 feet. the Pauba formation, including about 250 feet of hardpan — lithified The Temecula basin consists of both alluvial plains and fanglomerates, yellow and red arkoses, brown silts, and diatomite. sedimentary mesas. The Aguanga basin, which includes ishghtly younger than the Pauba are the Dripping Springs fanglom- ... „ " . , n ° . , . „' „ . erates, typically developed in arroyos in the strongly dissected similar alluviated valleys, consists chiefly of large areas Pauba fans. Shortly after the Dripping Springs deposition the of badlands. The basement highlands, though character- Nigger Canyon volcanic rocks were erupted. These consist of nephe- j ze d by steep slopes and deep canyons, haye many high- line basalt flows and dikes, and one or more pyroclastic cones The sta nding areas of subdued relief. Numerous stream ter- youngest deposits are alluvium, in places as much as 120 feet thick. D . . , ,, ,. , -,, . „ , The structure is complex and consists chiefly of high-angle nor- races, cut in both sediments and basement rocks, flank mal faults, most of which trend northwest. The major movements the Temecula River. occurred in the middle Pleistocene and were dominantly vertical. The climate of the Temecula region is Semi-arid, the Vertical movements of 3300 feet can be demonstrated, but throws „_„„„ „„„„„i „„;„f„n „r io ;„,a,~„ n„„„*.„;„~ „V,^fl^ , ... , . . „„„ . • „„. .. tr„,.;„„„f„i average annual raintall oi 16 incnes occurring cnietlv of several thousand feet more are not improbable. Horizontal " 6 XT , , ,, , m , ", '\ shifts do not appear to be greater than about 1000 feet, whereas between November and March. 1 he summers are hot and the major movements involved a general uplift, the Murrieta dry with temperatures commonly 110° F. or more. The graben block has been dropped more than 1500 feet below sea level winters, however, are normally mild, and freezing tem- Durine the Pliocene the Temecula region was a broad alluvial . « , x .■■ ■• . . , surface of low feiief with many inselberge. At about the end of the peratures are infrequent. In the basins snow is rare but on Agua Tibia Mountain snow may remain throughout * A Lo 8 s ta Angei r e s fessor ° f Geology ' Unlver8,ty of Southern California, thg winter and early spr i n g. Because of relief, slope (3) Special Report 43 ORANGE Vv, <$ LAKE EL SIN ORE COUNTY / f RIVERSIDE COUNTY Area mapped for this report MILES Figure 1. Index map showing the location of the Temecula region. facing, and small areal climatic differences, the vegeta- tion is varied. In the Temecula basin the most abundant plants are chamise, buckwheat, and prickly pear. In the Aguanga basin is a chaparral consisting primarily of chamise, black sage, and mangelar. On the bedrock slopes there is a chaparral of chamise, ceanothus, scrub oak, and manzanita, which is densest on north-facing slopes. Phreatophytic plants occur along fault lines and on alluvium where the water table is close to the surface. The geologic mapping of the Temecula region (about 150 sq. mi.) was done between November 1948 and June 1949 and involved about 4 months of field work. Aerial photographs- were available for the entire area. The writer expresses his appreciation for numerous suggestions to the following members of the Department of Geology, University of Southern California : Drs. Thomas Clements, K. O. Emery, W. H. Easton, R. H. Merriam, D. A. McNaughton. For the use of drafting and other facilities, the writer is indebted to the Depart- ment of Geology and the Allan Hancock Foundation, University of Southern California, and to the Illinois State Geological Survey. For suggestions as to the ages of the vertebrate fossils collected the writer is indebted to : Childs Frick, the late Chester Stock, R. A. Stirton, T. E. Savage, and Guy E. Hazen. G. Dallas Hanna kindly examined some samples of diatomite, and J. Harlan Johnson some samples oi algal limestone. Identifications of the fossil gastropods were made by W. 0. Gregg, and by A. B. Leonard. Teng- Chien Yen supplied a statement regarding the age oi these gastropods. PHYSIOGRAPHY Reed (1933) and Jenkins (1938, 1943) have includec the "Peninsular Ranges" as one of the major physio- graphic provinces of California. Topographically, the Peninsular Ranges may be divided, from west to eastj into three belts : (1) a terraced coastal belt underlain by Cretaceous and Cenozoh sediments, and deeply incised by erosion ; (2) a complex central highland consisting of many fault blocks standing at different elevations. The lowest blocks are sedi ment-filled valleys. Drainage shows a marked structural con trol; (3) a prominent eroded fault scarp which descends to an ari ° n 9 .°~- °'- S. .""\/ a 1 1 e y-\N evada- ...•• 1 SAN BERNARDINO.^ ■+ \ i \ ! I •j.... X s V e A 5 9 \ ~ o D e s e r t y ANCCLES / e s y \ Geomorphic Provinces of Southern California S S u '**-Tr '• B S I D E V Xq v" ° c> jf_t % *■ \ S * R ^jL - „ SO -,. _./ I j -.L L- ^ Scale 40 / '•••■•••? 80 Mile* after Jenkins, 1938 Figure 2. Geomorphic provinces of southern California. Aguanga Basin. The second large physiographic divi- iion is the Aguanga basin, comprising the eastern part >f the Temecula region (fig. 3). This basin consists of ieveral alluviated valleys, bounded in part by fault-line icarps, and separated by bedrock canyons. All of these /alleys are part of a single integrated drainage system vhich flows into the Temecula basin through Nigger Janyon. Aguanga Valley, in the southeastern part of the basin, s a broad, alluviated flat in the course of Temecula 3reek, and represents one of the baselevels suspended )etween a pair of bedrock canyons. The southwest side >f Aguanga Valley is a prominent fault-line scarp with veil-developed triangular facets. A parallel fault-line icarp forms the southwest boundary of Radec Valley, rhe course of Temecula Creek through Nigger Valley s chiefly the result of free-swinging between bedrock lodes, although faults in the Temecula arkose probably lave had some influence on this course. Lancaster Valley vas eroded along the basement-Temecula arkose contact it the north boundary of the basin. The Dripping Springs alcove is a large V-shaped re- intrant in the Palomar block. The boundaries as shown m plate 1 are partly fault-line scarps and partly the •esult of post-faulting deposition. The "badlands" in- ilude several areas of Temecula arkose, one of which !orms the "backbone" of Aguanga basin. Lewis and Wilson Valleys are mature pre-Temecula arkose valleys, langing as a result of the post-Temecula faulting and exhumation. Arkose remnants in Crosley Valley suggest a similar origin for the perched mature valleys of the Palomar block. Oak Mountain Barrier. The Oak Mountain barrier is defined as the bedrock ridge which separates the Temecula and Aguanga basins. It consists of the bed- rock blocks of Oak, Vail, and Dorland Mountains sep- arated by fault zones in Dorland Gap and in Nigger Canyon. The exact limits of the Oak Mountain barrier are difficult to define. Generally speaking, it could be considered a cross-faulted horst with much greater throw on the northwest side than on the southeast side. One series of cross-faults occurs between Oak and Vail Mountains ; in this zone of weakness Nigger Canyon has been eroded. Between Vail and Dorland Mountains is another fault zone ; the saddle produced here at Dorland Gap appears to be chiefly of tectonic origin. The struc- ture of the Oak Mountain barrier is shown in section C-C, plate 2. The erosion surfaces topping Oak and Dorland Mountains are about 2,600 feet above sea level, whereas apparently the same surface on Vail Mountain is about 600 feet lower. Adjoining Physiographic Units. The Perris block is an elevated plain with very low relief, due partly to erosion and partly to sedimentary fill. Above this surface many monadnocks and inselberge rise several hundred feet or more. Southwest of the Elsinore-Temecula trough the Santa Rosa plateau includes the southeastern part of the tilted Santa Ana block. This plateau surface re- Special Report 43 sembles the surface developed on the Perris block and apparently was formed at about the same time. The Palomar block is a huge horst of plutonic and meta- morphic rocks uplifted between parallel fault zones of the Elsinore fault zone. Its summit is a surface of very low relief. Similar erosion surfaces, occupying half- height positions on both flanks of the Palomar block, sug- gest uplift in two stages, or perhaps step faulting. Drainage. All the drainage from the Temecula and Aguanga basins passes from the basin areas to the ocean through Temecula Canyon. The main stream of the region is the Temecula River (or Temecula Creek), whose name changes in Temecula Canyon to the Santa Margarita River. The chief tributaries in the Temecula basin are Murrieta and Penjango Creeks, which follow the Mur- rieta trough and join the Temecula River close to the head of Temecula Canyon. In the Aguanga basin, the im- portant tributaries are Lewis, Wilson, and Arroyo Seco Creeks, which rise in areas of high elevation (and there- fore high rainfall) and contribute substantially to the annual flow. Only the largest streams are perennial, but many more flow continuously from November to June. Where the valleys are heavily alluviated, surface flow is uncommon, but underflow in the alluvium is important. Surface flow usually occurs where alluvium is thin or absent, as in bedrock canyons. Much of the physiographic history of the Temecula region can be determined by a study of the present streams. Low stream gradients characterize the following surfaces: (1) those developed on the soft Pleistocene sediments where baselevels are rigidly controlled by bed- rock canyons; and (2) exposed bedrock surfaces of low relief. The streams in (2) usually have a reach of steep gradients as the Temecula or Aguanga basin is approached. Stream piracy is an important process. The obsequent streams of the Santa Ana block have a tre- mendous slope advantage over the consequent streams and are eroding headward rapidly. The divide is shifting westward, and beheading of some of the consequents seems inevitable. A tributary which joins the San Luis Rey River near Pala has already captured a tributary ofj Penjango Creek, and further piracy is imminent. In Dor- land Gap the tendency is for more drainage to be di-i verted westward to reach the Temecula River directly rather than pursuing the circuitous route around Vail Mountain through Nigger Canyon. Vail Mountain (pi. 1) illustrates well the relationships of tributaries to a semi-annular trunk stream of medium gradient. The tr;b-| utaries of Arroyo Seco Creek, on the east side of Vail Mountain, have gentle to moderately steep gradients. Tributaries of Temecula Creek, on the west side of Vail Mountain, though starting at the same elevation as those! on the east side, plunge sharply to a baselevel several hundred feet lower. Topographic Evidences of Faulting. An analysis of the scarps of the Temecula region, using the criteria, of Blackwelder (1928) indicates that these scarps are; fault-line scarps rather than true fault scarps. The orig-, inal surface displacements were in Pleistocene sediments and the existing scarps of basement rocks were not exposed until a considerable thickness of those sediments had been removed by erosion. Generally speaking, the scarps in the metamorphic rocks and gabbro are char- acteristically flat with sharp convex sutures at the top. Those in intermediate plutonic rocks are gentler, with smoothly rounded sutures. In the Temecula region the development of fault-line scarps is controlled chiefly byj climate and rock type; the resulting slope would be the same whether the fault were normal or reverse (Hill, 1930, p. 161). After faulting and exhumation, the slope first becomes gentler by rotation about a point above the base of the scarp. In the interfluves, denudation is accomplished by weathering and sheet-wash. After the initial rotation to an inclination of 35 degrees or less, the denudational slope retreats parallel to itself anc tends to persist long after its base has left the trace oi the fault plane. BLOCK PLATEAU PHYSIOGRAPHIC UNITS TEMECULA REGION - — - MAIN BASIN BOUNDARIES UNIT BOUNDARIES BEDROCK CANYONS SCALE -o Figure 3. Physiographic units of the Temecula region. Elsinore Fault Zone — Mann Springs, both hot and cold, occur in straight-line series along many of the faults. Where there are associated scarps or sharp lithologic breaks, the springs are merely corroboratory evidence of faulting. But where such fea- tures are absent, the spring lines are of considerable value in delineating faults. Where there are no springs, fault lines may be shown by phreatophytic vegetation. Although most of the faulting in the Temecula region occurred at too remote a time for one to expect many sag features, such features may be seen along the Wildomar fault and along the east-trending fault which passes through Murrieta (pi. 1). Subsequent drainage is cer- tainly one of the most typical topographic expressions of faulting, and in the Temecula region, streams flowing for parts of their courses in fault zones are numerous. Alined saddles proved to be one of the most reliable cri- teria of faulting, especially in the Pleistocene sediments of the Aguanga basin, where offsets were too difficult to detect. Although landslides are not usually confined to areas of faulting, it was found that in the Temecula region, most landslides which do occur are in the areas of the strongest faulting. Other Physiographic Features. Badland topography is developed on the Temecula arkose throughout the Aguanga basin and in the extreme eastern part of the Temecula basin. Larger areas of badlands occur north of the Temecula region, in the Elsinore and San Jacinto quadrangles (Frick, 1921; Fraser, 1931). The sediments there are in part of the same age and source as the Temecula arkose. Exhumation of old bedrock surfaces and the removal of unknown thicknesses of Temecula arkose from the areas flanking the Temecula and Aguanga basins is evi- dent. The Temecula arkose now in fault contact with the gabbro of Dorland Mountain contains no gabbroic de- tritus. Therefore, Dorland Mountain at one time must have been covered completely by the Temecula arkose. The amount of Temecula arkose removed to produce the present topography was at least several hundred feet, possibly 1000 feet or more. Under conditions (as on Dor- land Mountain) where the unconsolidated Temecula arkose overlay the basement, stripping may have been complete — leaving no remnant of the sediment which for- merly buried this surface. Thus, the absence of Temec- ula arkose on an uplifted surface of the basement does not preclude its former presence there. The mechanism of exhumation in some places is illustrated very graph- ically. Near Aguanga, the southern part of Cienaga Rincon is subsequent, because it was eroded along a tonalite-arkose contact. The underlying tonalite block is tilted to the west and the stream in Cienaga Rincon has been uniclinally shifting to the west, following the slope of the basement surface. The exhumation process in op- eration may be seen along the highway just east of Radec Valley. Throughout Pleistocene time the Temecula region was characterized by intermittently changing baselevels, and the result is a complex series of stream terraces. The highest flat surfaces, which are outside the boundaries of the basins, are probably parts of the pre-Pleistocene ero- sion surface. The highest stream terraces are along the north wall of Nigger Canyon, high on the south flank of Oak Mountain, at an elevation of about 2300 feet. The broadest terrace on Oak Mountain is at an elevation of about 2000 feet. On the south wall of Nigger Canyon the terrace remnants are few and small. The presence of many faults and much gouge on the north side of Nigger Canyon probably accounts for the better expression of the terraces there. On the south flank of Oak Mountain, faulting has offset and tilted some of the higher terraces. The terraces of Pauba Valley, which were cut on the Pleistocene sediments, are at a lower physiographic level, and are therefore younger than the terraces in Nigger Canyon. Remnants of Pleistocene fans are best exposed in the Dripping Springs alcove. The Pauba fanglomerates, which were deposited by north-flowing streams, filled the alcove to a depth of several hundred feet. Diastrophism, accompanied by lowering of the baselevel in Temecula Creek, permitted dissection of these fans near the apices and in the lower reaches, leaving imposing midfan mesas (Eckis, 1928, p. 235). The Dripping Springs fanglom- erates were deposited in the arroyos cut in the Pauba fans. STRATIGRAPHY Basement Rocks As this investigation was concerned primarily with the younger sediments of the Temecula region, little detailed work was done on the metamorphic-granitic complex, which is referred to herein frequently as the ' ' basement ' ', or "bedrock". Most of the area of basement rocks in the Temecula region was mapped by Larsen (1948), and the basement geology on plate 1 is in part generalized and modified after his map. His memoir was drawn on freely for the following discussion of the basement rocks. Rocks believed to be of Paleozoic age have been found in the Peninsular Ranges north and east of the Temecula region (Larsen, 1948, p. 16). The only positive evidence of a Paleozoic age was obtained by Webb (1939, p. 199), who collected a tetracoral in talus at the base of a large marble bed in the upper quarry of the Winchester mag- nesite mine near Hemet. However, the usual criterion for assigning a Paleozoic age to many of these rock bodies is the degree of regional metamorphism — notably greater in this group than in the fossiliferous Triassic rocks. The Paleozoic rocks consist of mica schists and quartzites; locally, however, there are limestones, such as at the Crestmore and New City quarries near Riverside. All the rocks of Triassic age in the Santa Ana Moun- tains and vicinity are included by Larsen (1948, pp. 18-22) in his Bedford Canyon formation. This forma- tion occurs only in the western part of the northern Peninsular Ranges and consists of mildly metamor- phosed slates and argillites, with a few beds of quartzite and limestone. This formation is considered Triassic on the basis of sparse, poorly preserved marine fossils from a small area in the northern Santa Ana Mountains. Larsen (1948, p. 23) includes the Jurassic metamor- phics in his Santiago Peak volcanics, equivalent in part to the Black Mountain volcanics of Hanna (1926). These rocks are found in the western half of the northern Peninsular Ranges and are predominantly andesites and quartz latites with some rhyolites and probably some basalts. They form a pile of alternating flows, tuffs, and breccias. ... A little slate and quartzite were found. (Larsen, 1948, pp. 24-25). Special Report 43 to UJ £ £ z o o z ( ,- N < .ft t- UJ K m the Palomar horst and the Oak Mountain barrier, w-level fanglomerates are associated with the basin- unding faults both north and south of Aguanga. Sev- tl patches occur in Nigger Valley, and in Arroyo Seco, lich connects the Dripping Springs alcove with Nigger nyon. Gravels of this approximate level were exca- ted from both abutments of the recently completed til Dam at the head of Nigger Canyon. A filled channel ,s discovered while excavating for the spillway, and was necessary to put in a small concrete arch to span s channel. At the mouth of Nigger Canyon, gravels re found beneath the volcanics at the end of the ag- >merate-capped ridge about two hundred feet above i present stream bed. Other low level fanglomerates re mapped on the north side of Penjango Creek. In the Dripping Springs alcove, where the Pauba lglomerates are thick, younger fanglomerates were posited in arroyos cut in the Pauba fans. Elsewhere } Pauba formation was in places originally thin, d the post-Pauba dissection was thorough enough to nove much or all of the older fanglomerate before the unger fanglomerate was deposited. The Dripping •rings fan surfaces are always appreciably higher than i Recent alluvium, but exact differences in elevation tween younger and older fanglomerates and the allu- lm are difficult to state. The Dripping Springs fanglomerate can not be dis- tguished on a lithologic basis from the Pauba fanglo- srates. Although minor diastrophism occurred between s depositions of the two fanglomerates, the initiation Dripping Springs deposition was not necessarily the suit of that diastrophism. Instead, a lowering of base- re\ in the Temecula basin, possibly related to piracy at imecula Canyon was the cause of the dissection of the tuba fans and renewed deposition at lower levels. Thus ere was no appreciable change of source area between mba and Dripping Springs times. The Dripping Springs fanglomerate is strictly a super- ial deposit and the thickness probably nowhere exceeds few tens of feet. Although mild faulting and erosion curred between Pauba and Dripping Springs time, the gree of weathering of the contained boulders suggests at the formations are close to the same age. Nigger Canyon Volcanics The name Nigger Canyon volcanics is applied to a ries of tuffs, agglomerates, dikes and flows, which are und near the mouth of Nigger Canyon. Basalt of about e same age and composition crops out along Murrieta •eek about 2 miles northwest of Murrieta (Larsen, 48, p. 112). The volcanic rocks near the mouth of igger Canyon were extruded from a series of fractures ending N. 45° E. On the south side of the canyon outh is a cinder cone of buff tuffs and brick-red agglom- ates. Many bombs of scoriaceous basalt, up to several et across, are contained in the agglomerates, which irsen (1948, p. 112) believes are partly flow or welded ■eccias. The cinder cone was formed on the present ape of Vail Mountain, and rests directly on meta- orphic rocks. The pyroclastics were derived from a isure well up the flank of the mountain, and the cone is ymmetric, as a parasitic cone would be. The agglom- erates of the cone plunge steeply beneath the Recent alluvium, and the cone is covered with alluvium for several tens of feet above the base. The cone was formed and partly dissected prior to the last heavy alluviation. Several basalt flows are found less than a mile southwest of the cone and may have come out the same fissure as the pyroclastics. The toes of these flows have been eroded by lateral sweeping of the Temecula River while at the low pre-alluviation baselevel. On the same structural trend as the flows and the cinder cone is a northeast-trending ridge capped by a basalt flow, and agglomerates apparently identical with those of the cinder cone. The keel of the ridge is a fault which separates Temecula arkose on the northwest from metamorphics on the southeast. The fault is about coinci- dent with the northwest scarp in the agglomerates. Just east of this ridge, on the north wall of the canyon, and several hundred feet above the canyon floor, is a veneer of red agglomerate which appears to have been welded to the wall of the canyon. The agglomerates on the ridge overlie a small patch of water-worn gravels which can be seen only at the southwest tip of the ridge, more than 200 feet above the canyon floor. The petrology of these volcanics has been studied by Larsen (1948, pp. 111-113). He classifies the flows near the mouth of Nigger Canyon as nepheline basalts, and, notes their petrologic similarity to the basalt dike north- > west of Murrieta. The latter contains sparse but large (up to 3 cm) phenocrysts of glassy oligoclase in a fairly dense groundmass. The Nigger Canyon volcanics were extruded at two different times. They are of upper Pleistocene or sub- Recent age and are appreciably younger than the Pauba formation. The first extrusion occurred at about the end of Dripping Springs time when the Temecula River was flowing at a level at least 200 feet higher than at present, approximately at the spillway level of Vail Dam. The first agglomerates may have choked the mouth of the canyon and may have dammed the river long enough to produce the sharp turn that the river makes at this point. The second eruption occurred after the Temecula River had become entrenched more than 200 feet below its level at the time of the first eruption. The cinder cone was formed just southwest of the canyon mouth as were also the flows farther southwest. Faulting has been con- sidered as a means of explaining the difference in level of the volcanics on opposite sides of the river ; although there is evidence of some faulting in post-Nigger Can- yon time, displacements of several hundred feet are dif- ficult to substantiate. The Nigger Canyon volcanics are significant in that they indicate deep-seated readjustments in the Temecula region. They are located along the major transverse physiographic and structural break of the region — sep- arating the Temecula basin and the Oak Mountain barrier. Although a few earthquake epicenters have been plotted in this vicinity (Wood, 1947), the concentration is not as great as might be expected. Terrace Gravels and Recent Alluvium Terrace gravels occur at very low levels, especially just above the head of Nigger Canyon. Their low level and lack of induration suggest a very late Pleistocene or Recent age. 16 Special Report 43 Excavation for the foundation of Vail Dam revealed 20 feet of alluvium overlying the metamorphic bedrock. The thickness of this alluvium increases downstream and is as much as 120 feet in Pauba Valley. Recent allu- viation has been reported from numerous places in southern California, inland as well as along the coast. Alluvial backfilling of late Pleistocene valleys was found by Poland and Piper (1945) in the Los Angeles plain area. Similar alluviation has occurred along the south- ern California coast in the valleys of Santa Margarita, San Luis Rey, San Dieguito, and San Diego Rivers. Moore (1930) noted 100 feet of alluvium in Santiago Creek, east of Santa Ana. STRUCTURE The Temecula region, a portion of the Elsinore fault zone, includes the Temecula and Aguanga structural basins which are downfaulted blocks of a Mesozoic base- ment complex on which late Cenozoic continental sedi- ments have been preserved. Between these two basins is a horst, expressed topographically as the Oak Mountain barrier. Within the Temecula region the Elsinore fault zone widens from about 3 miles at the west boundary to more than 10 miles near Aguanga. In the western part of this region the Elsinore fault zone is marked chiefly by a structurally depressed area — the Temecula basin. South- east of the Temecula basin, however, the Elsinore fault zone is for the most part structurally positive, consisting of the Palomar horst flanked on the northeast by a relatively narrow graben. The Aguanga basin occupies the northwest end of this graben. In the Temecula region the individual faults are al- most invariably of the high-angle normal type. Move- ments have been chiefly vertical and throws of a mile or more are indicated. Horizontal movements are shown by a few faults, but horizontal displacements have probably not exceeded a few thousand feet. Many faults involve rotational movements. Although faulting of the Cenozoic sediments has been extensive, folding is uncommon. How- ever, near faults of strong throw, the sediments in places show drag. The regional trend of the Elsinore fault zone is ap- proximately N.45°W., and the strike of 60 percent of the faults mapped in the Temecula region is between N.40° W. and N.80°W. The present Elsinore fault zone was apparently origi- nally delineated at about the end of the Pliocene. How- ever, the major vertical movements did not occur until the middle Pleistocene. Smaller movements have con- tinued from the middle Pleistocene to the present. Previous structural studies in the Elsinore fault zone, all northwest of the Temecula region, are those of Eng- lish (1926), Larsen (1948), and Engel (1949). Major Structural Features of the Temecula Region The Temecula Basin. The Temecula basin, which is a structural as well as topographic basin, is bounded on the southwest by the eroded scarp of the Willard fault zone and on the southeast by the irregular scarps of the Pechanga fault zone. The hypotenuse of this roughly right-triangular basin is poorly defined because the topographic evidence of faulting is obscure. The Willard fault zone has been named by Engel (1949) to signify the bedrock displacements which mark the northeastern boundary of the Santa Ana Mountah from Lake Elsinore southeast. Although Engel shows th as a single fault, its extension into the Temecula regie appears as a zone of faulting (pi. 1). The Willard fau zone trends about N.45°W. and is one of the most pe sistent strands of the Elsinore system. The Wildomar fault, which was named by Eng (1949), extends southeast into the Temecula regio (pi. 1) beyond the Temecula River. Gouge zones nei the western boundary of the mapped area are near] vertical. The term "Wildomar horst" is applied here to tl upthrust block of bedrock and Temecula arkose, whic is best seen just northeast of former U. S. Highway 3S halfway between Wildomar and Murrieta. Its southwei boundary is the Wildomar fault, and a nearly paralle less extensive fault bounds it on the northeast (sec. A- A pi. 2). The horst is not expressed topographically soutl east of Murrieta. The name " Temecula-Elsinore trough" has alread been used by Larsen (1948, p. 3) for the entire lines valley extending from near Corona southeast beyon Temecula. For clarity it is suggested that the grabe northwest of Lake Elsinore be referred to as the ' ' Teme cal graben ' '. For the narrow downdropped block extern ing from near Rome Hill (Lake Elsinore quadrangle southeast to the Pechanga Indian Reservation (pi. 1 the name "Murrieta graben" is proposed. The Murrieta graben is a structural depression aboi 18 miles long, averaging a mile in width, and is include between the Wildomar fault and the Willard fault zon The basement surface in the graben dips southeast, an the thickness of the sedimentary fill increases in ths direction. The name "Pechanga fault zone" is proposed hei for the complex fault zone of great throw which bounc the Temecula basin on the southeast. Aguanga Basin. The Aguanga basin, in the nort! western part of the Agua Caliente graben, was mappc in detail for this report. The term "Agua Calien fault" has been generally applied to the fault boundir the Palomar horst on the northeast. Field study clear shows that this is not a single fault but a series of su parallel faults which have produced a graben. Th graben should properly be called the "Agua Calien graben ' ' to preserve the essence of the original name. The name "Aguanga fault zone" is proposed for tl fault zone marked by the prominent scarp south and we of Aguanga. South of Aguanga the main fault trenc N.62°W. but father west it joins a persistent fault trenc ing N.44°W. (pi. 1). The same zone of faulting trenc southeast and forms at least part of the northeast bounc ary of the Palomar horst. Exposures of some of the fau planes of this zone, directly south of Aguanga, sho northeast dips of more than 80 degrees. The Lancaster fault zone, along which Lancaster Va ley has been eroded, bounds the Aguanga basin on tl north. Strikes do not conform to the regional tren and the zone converges toward the Aguanga fault zoi to the west. Where the Lancaster fault zone crossi Highway 79, a horst marks the zone of faulting (pi. 1 Oak Mountain Barrier. Faults with many hundrec of feet throw bound the Oak Mountain barrier on tt west and east ; these have produced a horst transvers to the regional trend of the Elsinore fault zone. Elsinore Fault Zone — Mann 17 Nature and Magnitude of Displacements Criteria of Faulting. In the Temecula region, physi- raphic evidence must be relied on heavily to indicate llting, as direct evidence of faulting is sparse. How- ;r, detailed field study will usually reveal some sort direct or indirect evidence to support the physio- iphic evidence. Numerous breccia and gouge zones were located, ne of them many feet wide. At more than a dozen alities, the attitudes of fault planes and gouge zones jld be measured. Most of these faults were at or near sement-sediment contacts. Dislacements of strata were sn and measured in the Aguanga basin where the mecula arkose contains resistant marl and silt layers, milarly, many displacements were observed in the aglomerates. Slickensides were noted only in the first uble roadcut north of Radec. Less positive evidence faults may be represented by linear topographic mds of carbonate-cemented arkose. In general, high ps in the Temecula arkose are reliable indicators of arby faulting. Vertical Movements. At most places where it was ssible to measure the dips of the fault planes and uge zones, the dips were 70 degrees or more and e faults were normal. In the few reverse faults that re found the displacements were only a few tens of it. The preponderance of high-angle normal faults the Elsinore fault zone is also recorded by Engel 949) in the Lake Elsinore quadrangle. In the Oak Mountain barrier, the level summits of ik Mountain and Dorland Mountain are at an eleva- >n of 2600 feet ; Vail Mountain, topped by apparently e same erosion surface, is about 600 feet lower. At iny places minimum throws of basement-sediment ults may be obtained by determining the height of e fault scarp. This estimate may be increased by ratigraphic studies and by examination of well logs, it deep wells are so few that the data rarely indicate creasing this minimum by more than a few hundred et. The lava layer recorded in the Barnard no. 2 oil st (pi. 1) at a depth of about 2450 feet is correlated ith the Santa Rosa basalt capping Mesa de Burro and ogback. The minimum vertical displacement shown tween Mesa de Burro and the Murrieta graben is 00 feet. The basement surface in the Murrieta graben this vicinity is therefore more than 1500 feet below a level — clearly demonstrating absolute downdropping ther than a relative depression in a general uplift, riother oil test (Murrieta Valley Oil Co. no. 1) 1 mile uth of Murrieta Hot Springs, reached bedrock at »out 1025 feet ; at Murrieta Hot Springs basement rock at the surface. The Bennett water well (pi. 1) drilled June 1953 in the graben just northeast of the Wildo- ar horst apparently encountered about 10 feet of isalt at a depth of 1210 feet and went into the base- ent at a depth of 1355 feet. The greatest vertical displacements are probably ong the Pechanga fault zone in the Pechanga Indian eservation. The surface relief from Temecula Valley > the top of Agua Tibia Mountain is about 3000 feet, it as Temecula Valley contains a considerable amount ' fill, the actual vertical displacement in the basement irface may be several thousand feet more. A water well drilled in 1951 by the U. S. Navy (pi. 1) in Pauba Valley, a few hundred feet northeast of the Wildomar fault, went to a depth of 2478 feet without reaching the basement. About 2 miles northwest of Murrieta, in the Murrieta graben, basement rocks are exposed at the surface. East of Murrieta, in the Barnard no. 2 oil test, basalt was encountered at a depth of about 2450 feet. As the com- plete driller's log was not made available, the exact depth-to-basement could not be determined. This test hole is not in the Murrieta graben, but in a higher block northeast of the "Wildomar fault ; thus a minimum depth-to-basement of 2500 feet in the graben near the test hole seems reasonable. It is believed that the base- ment surface in the Murrieta graben is of low relief, similar to that exposed nearby on the Santa Rosa pla- teau. Assuming a regular dip of the basement surface and the absence of warping and faulting, this sloping surface would reach a depth of 5000 feet near Temec- ula, and 8000 feet at the southeast end of Temecula Valley. Another possible interpretation is that the max- imum depth occurs near Temecula and the basement surface slopes upward to the southeast beneath Temec- ula Valley. The reversal in slope or a sharp decrease in depth might be associated with the cross-faults which formed Rainbow Gap (pi. 1). On the basis of the above evidence it seems likely that the throw along the Pechanga fault zone is a mile or more. Although warping of the basement surface may explain part of this throw, many northeast-trend- ing faults indicate that faulting has been the chief cause of this sharp topographic break. Furthermore, the align- ment of the Nigger Canyon volcanics along several of the northeast-trending faults indicates profound frac- turing. On plate 1, a number of faults are shown to intersect without offset. It is acknowledged that this is a special case and would occur only rarely in nature. Some of the faults were determined purely from physiographic evidence, and the movements may have been too small to be detectable by surface or aerial photographic studies. The faults flanking Dorland Mountain are believed to fit the necessary special conditions inasmuch as the fault planes are close to vertical, and the movements have been almost exclusively vertical. Horizontal Movements. Evidences of horizontal move- ments in the Temecula region are uncommon, and measured displacements are not more than about 1000 feet. A fault northeast of Oak Mountain (pi. 1) has a horizontal displacement of about 1000 feet, as shown by offsets in stream courses. On Vail Mountain, an isolated remnant of Temecula arkose shows an offset of about 600 feet. Horizontal slickensides occur in the double roadcut one mile north of Radec. There are a few other faults along which there are indications of horizontal displacement, but the field evidence is, for the most part, inconclusive. Rotational Movements. Faults with changing throw along the strike are common in the Temecula region. Comparison of the southeast slope of the basement sur- face in the Murrieta graben with the basement slopes on the Santa Rosa plateau and on the Wildomar horst strongly suggests that the movements on both the Wil- 18 Special Report 43 lard fault zone (acting as a unit) and the Wildomar fault have been rotational. In the Aguanga basin the large fault south of the Lancaster fault zone decreases in throw to the west as do many other west-trending faults of this basin. Age of the Faulting Northwest-trending structures in the Temecula region probably date back at least to the Paleozoic (Larsen, 1948, p. 119). However, in this region it is difficult to demonstrate Cenozoic diastrophism before the deposition of the early Pleistocene Temecula arkose. In Crosley Valley, cobbles in the Temecula arkose may indicate that the central part of the Palomar block had at least mod- erate relief at the start of the Pleistocene. Engel (1949) notes that the first moderately strong movements along the Elsinore fault zone were in Plio-Pleistocene time, and it may be that the Palomar horst was upfaulted at this time. The most profound faulting in the Temecula region occurred during the middle Pleistocene, apparently con- temporaneously with the Coast Range or Pasadenan orog- eny which was widespread in California. This faulting produced great displacements in the basement surface and in the Temecula arkose, but it has not disturbed the Pauba fanglomerates. The present relief dates largely from the middle Pleistocene displacements. In the late Pleistocene there were minor movements in the Temecula region along pre-existing fault lines. During the late Pleistocene several periods of faulting are evident. In the Dripping Springs alcove, several northwest-trending faults of small displacement may be traced through the Pauba fanglomerates, but not through the Dripping Springs fanglomerates. North and east of Vail Dam some of the higher stream-cut terraces have been faulted and tilted. In the graben 2 miles north of Aguanga a few patches of fanglomerates have been downfaulted. Very late movements are shown by faulted low-level fanglomerates in Nigger Valley. The straight northwest boundary of the agglomerate-capped ridge near the mouth of Nigger Canyon suggests renewed movements along the major transverse fault which previously had downfaulted Temecula arkose against the metamorphics of the basement. Two northwest-trending faults have also disturbed this agglomerate. Faulting, especially along the Wildomar fault, has continued to the present. The exhibits of the Rancho Santa Margarita vs. Vail litigation contain photographs of sand craters which were formed in the alluvium of the Temecula River along the trace of the Wildomar fault. These apparently were a result of the San Jacinto earthquake of 1918. On December 4, 1948, while the field work for this investigation was in progress, a strong earthquake shook the Temecula region. The epicenter was located in Coachella Valley. In Temecula, bottles were knocked to the floor from shelves alined northeast but not from those alined northwest. A few ceiling cracks, oriented north- west, were observed in one building. At the time of the earthquake (4:44 P.M., PST) the writer was walking on the alluvium of the Temecula River about one mile west of the bridge of Highway 71. The alluvium did not noticeably transmit the seismic shocks. MINERAL RESOURCES Soil Agriculture and cattle raising are the chief industr of the Temecula region ; therefore, the most imports mineral resource is the soil. In the Temecula basin, so suitable for farming have formed on Recent alluviu on the Pauba formation, and on the Temecula arko The chief crops are wheat, oats, barley, and alfal which are usually farmed dry. Small areas in Pauba a Santa Gertrudis Valleys are irrigated, and in those v leys alfalfa, peaches, and truck crops grow well. Sc on the Pauba formation tend to become hard due to ir oxide cementation, but deep plowing and treatment wi ammonia keep the soil loose. In the Aguanga basin only the Recent alluvium farmed extensively as slopes eroded in Pleistocene forn tions are usually too steep. Dry farming is succesi even in alluvial fingers of the badlands. Some of t fingers are irrigated by portable sprinkling systems Those areas not under cultivation and those plant to forage crops are devoted to grazing several thousa head of cattle. Water Next in importance only to the soils are the surfi and ground waters of the Temecula region. The wal resources were studied by Waring (1919) in conjuncti with a larger investigation of the drainage basins of t San Jacinto and Temecula Rivers. The California Di sion of Water Resources has recently completed a surv of the ground water resources of the Temecula Rn drainage basin. Voluminous data on water resources the Temecula region and vicinity were collected dur the water rights litigation between Rancho Santa IV garita and the Vail Company. The litigation continu for 3 years and the records of testimony and exhib aggregate several tons. Parts of these data were « suited during the present investigation; however, a < tailed water resources study would require a thorou analysis of this information. Although the water : sources were not studied in detail for this report, c< siderable attention was given to the structural contro ground water movements. Springs are common along faults. Some are fou along the contacts between basement and sedimenta rocks ; others are found entirely in sediments, where t faulting is less obvious. Many of these springs have be developed for domestic supplies, for watering cattle, a for irrigation; many remain undeveloped. The Wildomar fault (pi. 1) is an important barr to ground-water movement. In the Temecula basi ground water moves southwest under both water tal and artesian conditions. At the Wildomar fault, groui water movement is effectively stopped and a groui water cascade is produced. An obvious result of this c( dition is the line of springs along the northeast edge i Murrieta and Temecula Valleys. Even though the hi water table northeast of the Wildomar fault may I reach the surface, its effects on vegetation may still noticeable. In the deeper aquifers of the Temecula arkose, 1 Wildomar fault creates areas of artesian flow in Pau and Santa Gertrudis Valleys, and also about a mile noi of Temecula. Though some of the wells no longer flc these are still areas of high water levels. Blsinore Fault Zone — Mann 19 Recharge into the Murrieta graben is poor, except in e Recent alluvium. In Temecula Valley, Waring 919) shows the water table 80 feet below the surface st southwest of the Wildomar fault. It does not appear cely that large water supplies will be obtainable from e Pleistocene sediments of the Murrieta graben. Many of the large capacity wells are in the alluvium Pauba Valley, where, despite recent faulting, hy- aulic continuity of the shallow material has not been ipaired. Elsewhere it is to be expected that the freely charged alluvium will reliably offer larger supplies an the complexly faulted older sediments. )t Springs Hot springs are found along both the San Jacinto and isinore fault zones. Murrieta Hot Springs is a large alth resort east of Murrieta. The springs issue along large east-trending fault along which the Temecula kose has been down-faulted about 1000 feet against e basement. The springs have temperatures as high as 6°F and are mineralized chiefly with sodium chloride, milar waters are used for bathing at Temecula Hot >rings, about a mile to the southwest, but reportedly e cooler. Sand and Gravel Sand and gravel to a depth of several tens of feet are und in all the alluvial valleys. Large quantities from rroyo Seco were used in the concrete for Vail Dam. lmerous other sites for gravel pits could be located. Granodiorite gruss has been used extensively for road aiding, and there are many places where this "decom- >sed granite" could be exploited. Rock At one time unweathered Woodson Mountain grano- orite in large residual boulders was quarried near smecula for use as a building and monumental stone, mee posts of this rock are still being used. The coarse ?uanga tonalite and the San Marcos gabbro or "black anite" would be excellent for monumental stone, lere are several favorable sites for quarries. Clay The Wildomar kaolin deposit has been mined for many ars although the quantity removed has been small- — ly about 150 tons per year. If the demand for such ly increases there is a bed of similar material in the ?uanga basin just north of the Dripping Springs inger Station which could be exploited. Diatomite A bed of fairly pure diatomite crops out near the top the mesa due north of Temecula. It is about 3 or 4 et thick and appears to be fairly extensive. It is not )rked commercially at present. Oil and Gas At least two oil tests have been drilled on the mesa tween Murrieta and Murrieta Hot Springs. Murrieta alley Oil Co. no. 1 was drilled in 1923 on the south side the highway near Murrieta Hot Springs. It was drilled 1120 feet after having reached basement at about 1015 et. Barnard no. 2 was started in 1938, and in the sum- er of 1949 had been drilled to about 3300 feet. The mplete log of Barnard no. 2 was not made available it the driller's log indicated a 16-foot flow of lava at a depth of about 2450 feet. At a depth of 3300 feet it seems certain that the well has penetrated several hun- dred feet of basement rocks. Nevertheless, it is planned to continue drilling. Terrell no. 1 was drilled in Radec Valley in 1947. This oil test was started in Temecula arkose within a few hundred yards of a tonalite outcrop, reached the base- ment at 312 feet and was drilled to a total depth of 2588 feet. The Temecula arkose-basement contact is clearly shown on the electric log, a copy of which was examined by the writer. The well is reported to have trapped a reservoir of gas under high pressure. No marine sediments were found in the Temecula region, although there are marine Paleoeene sediments near Elsinore. Marine sediments may yet be found in the deep fill of the Temecula basin, but their presence in the Aguanga basin is unlikely. LATE CENOZOIC GEOLOGIC HISTORY Pliocene. Early in the Pliocene the northern end of the Peninsula Ranges was apparently in late maturity. The "early land form" of Dudley (1936) had been heavily alluviated by Paleoeene and possibly later sedi- ments. Above broad alluvial plains inselberge rose sev- eral hundred feet, but they supplied very little clastic material larger than sand. Bellemin (1940, p. 670) re- ports that during the early Pliocene the Perris block was not an important contributor of cobbles to conglom- erates in the Puente Hills. The Mt. Eden beds of late lower or early upper Pli- ocene age (Frick, 1921) represent this sandy deposition in the San Jacinto region. In the Puente Hills the Pliocene consists of the sandstones and siltstones of the Repetto and Pico formations (Dudley, 1943). Local uplift in the San Jacinto region may have caused a change from sandy deposits of the Mt. Eden to gravelly deposits of the San Timoteo (Fraser, 1931). During Pliocene time the drainage of the Perris and San Jacinto blocks was probably northeast or north, as suggested by the following evidence : (1) the Mt. Eden beds are found only on the northwest flank of San Jacinto Mountain, the probable source area ; (2) the Mt. Eden beds now dip northeast and rest upon a base- ment surface which slopes northeast. This inclination is not easily explained by tilting ; (3) the two erosion surfaces near the top of San Jacinto Moun- tain described by Fraser (1931, p. 503) slope northeast. The present writer suggests that the highest surface (ele- vation 10,f>00 feet) was eroded during Mt. Eden time. Tahquitz Valley (elevation 8100 to 6500 feet) may have been formed following the uplift which resulted in the deposition of the San Timoteo beds, as suggested by the faulting which Fraser (1931) records for the Mt. Eden- San Timoteo interval. No Pliocene sediments have yet been found in the Temecula region, or anywhere else in the Elsinore fault zone between Aguanga and the northern part of the Temescal graben. It was established by Bellemin that the Santa Ana Mountains contributed almost no cobbles to the lower Pliocene conglomerates of the Puente Hills. There is little evidence that the Santa Ana Mountains were upfaulted during the Pliocene before the end of that epoch. The uplift which occurred in the Mt. Eden- San Timoteo interval was apparently an uplift of the Peninsular Ranges block as a unit along the eastern boundary faults. 20 Special Report 43 Plio-Pleistocene. The Santa Rosa basalts appear to have been extruded upon a surface of low relief formed at about the end of San Timoteo (late Pliocene) time. Near Temecula this surface is underlain in part by Paleocene sediments and in part by bedrock. The Santa Rosa basalts could be of any age from Paleocene to lower Pleistocene if stratigraphic position alone were consid- ered. However, freshness of the basalt, topographic posi- tion, and probable contemporaneity with wide-spread volcanism suggest a late Pliocene or early Pleistocene age. Not long after the Santa Rosa basalt extrusions the first important uplift of the Santa Ana block took place. Engel (1949) gives the age of these movements as Plio- Pleistocene. The Peninsular Ranges block continued its upward movement along the eastern boundary faults and continued its tilting to the west. The Perris block was relatively depressed and tilted northwest between the Santa Ana and San Jacinto blocks along the Elsi- nore and San Jacinto fault zones. The Elsinore-Temec- ula trough was apparently only a minor feature at this time, but the Palomar block was uplifted to form a long narrow horst. Early Pleistocene. Relative depression of the Per- ris block permitted accumulation of the Bautista and Temecula formations. These formations were derived from the San Jacinto Mountain block and vicinity and they buried the southeastern part of the Perris block; streams probably flowed southwest to the ocean across the low southeastern end of the Santa Ana block which had been tilted south during the Plio-Pleistocene uplift. The La Habra conglomerate was derived largely from the Puente Hills (Dudley, 1943), although the Santa Ana Mountains may have contributed some detritus. Probably during the deposition of the Bautista beds the prominent southwest bench (elevation ca. 5200 feet) on San Jacinto Mountain was formed, as suggested by its slope to the southwest, the direction of drainage during Bautista-Temecula time. At the end of early Pleistocene time, the northwestern part of the Peninsular Ranges was chiefly an alluvial plain formed at the top of the Bautista-Temecula sedi- ments. San Jacinto Mountain, Palomar Mountain, and the northwestern end of the Santa Ana Mountains were apparently inselberge. The area just southeast of the Perris block, as suggested by the present topography, was probably relatively high, with thinner sediments and more inselberge. Middle Pleistocene. The mid-Pleistocene orogeny profoundly affected the Temecula region. Uplift and tilt- ing westward of the provincial block continued, with further relative depression of the Perris block. The Santa Ana Mountains were uplifted and tilted south, while the Elsinore-Temecula trough was being formed by the downdropping of basement blocks more than a thousand feet below sea level. Though relatively depressed, the Perris block was up- lifted with reference to sea level, and its exhumation was started. As exhumation proceeded, downfaulted areas were probably filled continuously. Major streams may. not have been affected immediately by the uplift, but probably became antecedent and maintained a southwest direction of flow. As exhumation continued, the Santa Ana Mountains were intermittently uplifted .. and tilted. The higher erosion surfaces of the Santa Mountains are described by Engel (1949) who notes thi they are all tilted south or southwest; each surface lower and farther southeast than the next older surfac In contrast, the Perris block was stable, at least durir and after the erosion of the Gavilan-Lakeview surfai which is apparently horizontal. During a static bas level the Perris surface was formed. The Temecu River, which may have been flowing across buried Oj Mountain, was superposed at Nigger Canyon ; its dow cutting is marked by many terraces on Oak Mountai The Gavilan-Lakeview and Perris surfaces probably hi equivalent terraces in Nigger Canyon, but subsequei downcutting has obscured the relationships there. The San Jacinto River, after being superposed b tween tAvo inselberge of metamorphics, became e; trenched at Railroad Canyon. While the Perris surfai was being eroded, the San Jacinto River did not ha' sufficient elevation to flow directly across the Santa Ai Mountains as it had during the formation of the Gavila Lakeview surface. Instead, the trend of Railroad Cany( suggests it may have flowed southeast in the Elsinoi Temecula trough to join the Temecula River, which a parently left the trough through Pechanga Gap. Durh the formation of the Perris surface, the Santa Ro surface, which slopes northeast, was exhumed by streai flowing northeast to join the subsequent drainage the Elsinore-Temecula trough. The Santa Rosa surfi dates from pre-Paleocene (?) time and was re-expos by stripping of several hundred feet of sands and gn els and the overlying Santa Rosa basalt flows. During the exhumation, the Santa Ana River, whi had kept north to avoid the metamorphic core of t Santa Ana Mountains, vigorously maintained its anl cedent course. Earlier in the exhumation it probab had been a superposed stream. Owing to relatively rap incision, the Santa Ana River developed a subseque tributary system which eroded headward in the Elsinoi Temecula trough and captured first the San Jacin River, then the Temecula River. An apparent elbow capture just downstream from Railroad Canyon (La Elsinore quadrangle) may have resulted at this time. Early Late Pleistocene. During the early late Pie tocene time the Temecula region was the scene of ii portant drainage changes. Although the sequence events is not completely clear, the writer tentatively sv gests the following outline of events. A possible increase of rainfall initiated deposition the Pauba formation after large blocks of basement h been exhumed. Large fans were formed in the Drippi Springs alcove and elsewhere in the Aguanga basin, stream flowed from the Aguanga basin through a sup< posed course at Nigger Canyon ; it had to flow in t Elsinore-Temecula trough to Santa Ana Canyon, as t exit at Temecula Canyon was not yet in existence. T main Pauba fan, with its apex at the mouth of Nigg Canyon, was developed with reference to an east-w< axis of symmetry, showing no relationship to a li joining Nigger and Temecula Canyons as does the pr> ent Temecula River. The hardpans suggest that t climate was seasonally dry and the drainage restrict* The major ancient subsequent stream, which is nam here the Pauba River, was joined by the San Jacir River just below Railroad Canyon. The Pauba Rfr Elsinore Fault Zone — Mann 21 is probably confined to the northeast side of the mgh by huge alluvial fans spreading northeast from ; scarp of the Santa Ana Mountains. This river prob- ly flowed through the bedrock gap just east of Elsinore d up the trough, roughly following the present course Temescal Wash. The waters from the present drain- e area of Penjango Creek at this time may well have wed out Pechanga Gap just south of the Pechanga dian Reservation. The climate toward the end of Pauba time may ve been wetter than during earlier Pauba time, as sug- sted by the presence of fairly pure diatomite deposits, issibly at the end of Pauba time, sedimentation in a te or lakes on the Perris block produced the level val- I floors near Hemet. Such a lake, though possibly not the same age as suggested here, was previously sug- sted by Larsen (1948, p. 13). Headward erosion in Temecula Canyon reached the imecula basin presumably near the end of Pauba time. ie Pauba River was captured quickly and the Temecula sin was again dissected. The factors which accelerated adward erosion along the course of Temecula Canyon e as follows : (1) The canyon is cut in Bonsall tonalite which forms a narrow screen between the Bedford Canyon metamorphics and the Woodson Mountain granodiorite. Contact metamorphism is greatest in these thin screens. (2) Larsen (1948, p. 60) states: "Although the fresh Bonsall tonalite is a rather hard rock, it is more readily disinte- grated by weathering than most of the other granitic rocks of the area." (3) Faulting along the canyon course is suggested by: (a) the straight contacts of the basement rocks; (b) a trend of N. 45° E., one of the prominent joint directions; (c) an offset erosion surface, which is higher southeast of the can- yon than northwest of it. ie stream valleys in the Pauba mesa north and east of imecula in their upper courses trend west or a little nth of west (pi. 1). As these valleys approach Mur- ;ta Creek they curve and flow southwest, suggesting dows of capture. Before the major capture at Temecula tnyon, there may have been temporary diversion of irt or all the drainage of the Temecula basin through linbow Gap — a fault zone which apparently has been sdified by erosion of a throughgoing river. At the same time or slightly before the capture at smecula Canyon, there was diastrophism in the Elsinore ul'c zone. Minor faulting occurred in the Dripping >rings alcove. As a result of faulting at the end of luba (early late Pleistocene) time, it is suggested here, e basin of Lake Elsinore was formed. The huge fans lich had been deposited along the scarp of the Elsinore ountains during Pauba time were downfaulted. This gging caused the San Jacinto River to be diverted into e newly formed basin, creating a lake in this basin, id leaving a wind gap just east of the towri of Elsinore. a outlet was formed on the northeast lip of the lake isin and the overflow again joined the northwest-flow- g subsequent drainage. The apices of these fans were )t downdropped ; they were subjected to strong erosion, it a few patches remain (Engel, 1949, map). Latest Pleistocene. After considerable dissection of ie Pauba formation, the Dripping Springs formation as deposited during a period of relative crustal stabil- y. During Dripping Springs time, terraces were formed i Nigger Canyon, the Temecula basin, and Temecula Canyon. At about the end of Dripping Springs time the first extrusion of the Nigger Canyon volcanics occurred. A large cinder cone at the mouth of Nigger Canyon may have dammed the Temecula River temporarily. Erosion probably quickly cut through this cone, however, and Nigger Canyon was cut down about 300 feet in response to a lowering of baselevel in Temecula Canyon. Several paired terraces flanking the Temecula River in the Te- mecula basin attest to the fact that this downward ero- sion was not at a uniform rate. The Quaternary terrace gravels (pi. 1) represent one of the lowest temporary baselevels. Just before Nigger Canyon was cut to its lowest level, there was another eruption of flows and pyroclastics at the mouth of Nigger Canyon. The cinder cone was a result of this eruption. Further erosion dissected the cone and removed the toes of the flows. Recent. The latest event in the Temecula region has been alluviation, especially in the basin areas. In Pauba Valley, well records indicate this alluvium is as much as 120 feet thick. Diastrophism has continued throughout the late Pleistocene and up to the present, as indicated by Recent faulting. However, in the Temecula region, latest Pleistocene and Recent faults with more than a few tens of feet of displacement are rare. Summary of Late Cenozoic Events, Temecula Region and Vicinity. Pliocene Broad alluvial surface of low relief with inselberge. Perris block and Santa Ana Mountains low. Mt. Eden beds deposited. Highest erosion surface on San Jacinto Mountain formed. Drainage northeast or north. Upfaulting of San Jacinto Mountain block. San Timoteo beds deposited. Tahquitz Valley formed. Drainage northeast or north. Plio-Pleistocene Santa Rosa basalt extruded upon a surface of low relief. First important uplift of Santa Ana Mts. along Elsinore fault zone. San Jacinto Mtn. uplifted, Perris block depressed. Palomar Mtn. uplifted. Early Pleistocene Deposition of Bautista-Temecula sediments. Southwest bench formed on San Jacinto Mtn. Drainage southwest across Perris block and Temecula region. Broad alluvial surface formed with relatively few inselberge. Middle Pleistocene Pasadenan orogeny. Uplift and exhumation. San Jacinto Mtn., Santa Ana Mts., Palomar Mtn. uplifted ; Perris block up- lifted but relatively depressed. Elsinore-Temecula trough downfaulted. As exhumation proceeded, high erosion surfaces in Santa Ana Mts., Gavilan-Lakeview surface, high terraces in Nigger Canyon eroded. Perris and Santa Rosa surfaces formed, also terraces in Nigger Canyon. Santa Ana River developed subsequent tributary in the Elsi- nore-Temecula trough, captured San Jacinto and Temecula Rivers. Early late Pleistocene Pauba deposition. Faulting. Stream eroding headward at Temecula Canyon cap- tured ancient Pauba River. Basin of Lake Elsinore down- faulted. Dripping Springs fanglomerates deposited. Terraces formed in Nigger Canyon, Temecula Canyon, and Pauba Valley. Latest Pleistocene First eruption of Nigger Canyon volcanics. Erosion. Terraces formed in Pauba Valley. Second eruption of Nigger Canyon volcanics. Recent Alluvial deposits up to 120 feet thick. Faulting. Minor faulting continued throughout late Pleistocene and Recent. 22 Special Report 43 REFERENCES Bellemin, G. J., 1940, Petrology of Whittier conglomerates southern California : Am. Assoc. Petroleum Geologists Bull., vol. 24, no. 4, pp. 649-671. Blackwelder, Eliot, 1928, The recognition of fault scarps : Jour. 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