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Home , Transverse Ranges

A. K. BAIRD ^ A o' WOODFORD | Geology DePartment, Pomona College, Claremont, 91711 K. W. BAIRD '

Transverse Ranges Province: A Unique Structural-Petrochemical Belt across the System

ABSTRACT relate the system to concepts of global or plate tectonics (Atwater, 1970; Suppe, 1970; Hill, 1971b; Yerkes and Campbell, 1971). The San Gabriel and San Bernardino mountain ranges of Though these latest concepts have been widely discussed, only southwestern California, and associated mountains and basins diagrammatic interpretations that relate directly to problems of the westward to the Pacific Ocean, make up a unique east-trending Transverse Ranges Province have appeared so far in the literature geomorphic, stratigraphic, petrologic, and structural belt 400 km (for example, Anderson, 1971). Implicit or explicit in some of these long that is offset only a few tens of kilometers right laterally by discussions, which interpret the San Andreas zone as a plate northwest-striking faults of the San Andreas type. Spot correlations boundary (and a transform fault), is the idea that the Transverse across these faults, suggesting displacements of hundreds of Ranges are a geologically new feature, rotated and uplifted by the kilometers, perhaps have other explanations. Within the transverse most recent movements associated with southern and Baja ranges and basins, the east trend is shown by the general petrology, California tectonism and opening of the Gulf of California. the crystalline rock patterns, pre- and post-batholithic structural It is not the intent of this paper to redescribe, evaluate, and features, and batholithic chemical patterns. The east-west unity is criticize earlier studies. Rather, we wish to examine some of the especially striking west of the San Andreas fault, but it is also evident evidence bearing on the antiquity of the Transverse Ranges Province in the central and southern , east of that and how this province is related through time to adjacent provinces fault. of . We conclude that this belt has existed for a The Salton Trough and the southern boundary of the Transverse long time with the same transverse orientation, and that no great Ranges Province appear to be the most important provincial lateral separation — certainly not hundreds of kilometers — has boundaries in southwestern California. West of the San Jacinto occurred across this belt along any or all of the faults of the San fault, which is just southwest of the San Andreas fault and nearly Andreas system acting singly or together. To substantiate this parallel to it, the Transverse Ranges Province is bounded on the conclusion, we describe the geology under four headings: (1) south by the Malibu Coast-Cucamonga fault zone. At and just east pre-batholithic rocks and structure; (2) batholithic rocks and of the San Jacinto fault, the southern boundary fault zone is structure, chemical and age distributions; (3) post-batholithic rocks displaced by faulting 30 to 40 km to the southeast, and is continued and structure; and (4) structural development through time. as the Banning fault. East of the eastern (Mission Creek) branch of Much of the information assembled is not new, and most of it is the San Andreas fault, east-trending faults are present, but the San the work and resultant ideas of others. Most of the pertinent earlier Bernardino Mountains rocks and structures merge into the work was summarized by Bailey and Jahns (1954) and Jahns (1954). southeast-trending Little San Bernardino Mountains. Some of our compilations have relied heavily upon the mapping of T. W. Dibblee, Jr., of the U.S. Geological Survey. Most of the more INTRODUCTION general stratigraphic and structural features on which we rely are Along the entire mapped length of the San Andreas fault zone, shown on the Santa Ana, San Bernardino, and sheets of from to Mexico, no other belt of rocks, the Geologic Map of California (Rogers, 1965, 1967; Jennings and structure, and geomorphology similar to the Transverse Ranges Strand, 1969). Province crosses the zone. This has been clearly stated earlier by Allison (1964) and Gilluly (1970). No offset equivalent of the GEOGRAPHIC NOMENCLATURE eastern (San Bernardino Mountains) part of the Transverse Ranges Province is known across the San Andreas fault zone to the The Transverse Ranges Province is usually described on a northwest. No offset equivalent of the western (San Gabriel—Santa geomorphic basis as made up of the chains of ranges and valleys Ynez Mountains) part of the Transverse Ranges Province is known extending from the and Channel Islands across the fault zone to the southeast. The western part of the eastward through the San Bernardino Mountains (Fig. 1). Problems Transverse Ranges Province appears to offset, left laterally, a major arise, however, in defining accurate limits. The southern boundary boundary (the Newport-Inglewood zone) between granitic and from the coast to the San Jacinto fault is sharply delineated against oceanic basement terrains, though the northward continuation of the Province (including the ) by the wholly crystalline oceanic bedrock has not been discovered. The the Malibu Coast—Cucamonga fault zone (Fig. 2); east of the San province, therefore, has crucial implications for understanding the Jacinto fault, no line so prominent is evident. The northern structural evolution of southern California. boundary is poorly defined on both the extreme west, where the Development of ideas about the movement history of the San province joins the Coast Ranges Province, and on the extreme east, Andreas fault (and the other parallel faults that, with it, make up the where the San Bernardino Mountains merge with the San Andreas system) has proceeded from the original concept of Province. The north edge of the , at and near large-scale right-lateral slip proposed by Hill and Dibblee (1953), the San Andreas fault, and the north edge of the San Bernardino through numerous studies along various segments of the faults in Mountains, however, provide a sharp geomorphic contrast with the attempts to document offset through time, to the current efforts to considerably lower Mojave Desert plateau to the north. It is unclear how far eastward the province extends. Some of these boundary * Present address: U.S. Geological Survey, Menlo Park, California 94025. problems are considered later in this paper.

Geological Society of America Bulletin, v. 85, p. 163-174, 9 figs., February 1974

163

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PRE-BATHOLITHIC ROCKS conglomerate dips gently north and overlies gneiss. This east-west line of unconformity has been traced for more than 6 km, in and out Distribution of the ravines on the; south slope of Sugarloaf Mountain (J. F. One of the more striking aspects of areal geology in southern Richmond, 1973, personal commun.). Westward in the San California is the absence of rocks of known or suspected Bernardino Mountains and San Gabriel Mountains, east-striking Precambrian age in the Peninsular Ranges Province. In view of the carbonate and quartzite sequences occur, but no fossils have been extensive radiometric dating programs (carried out mainly by the found (Alf, 1948; Baird, 1956; Ehlig, 1958). South of the Malibu California Inst. Technology and the U.S. Geol. Survey), this absence Coast-Cucamonga fault zone, in the Peninsular Ranges Province, appears to be real. All known, or suspected, exposures of rocks of this type are unknown, except for small bodies such as those Precambrian rocks lie north of the Malibu Coast-Cucamonga fault in the Riverside area, in the San Jacinto—Santa Rosa Mountains, and zone or north or east of the Banning fault (Fig. 3; see Silver, 1971, for in northern Baja California. a discussion of the ages of the Precambrian rocks). Precambrian In contrast, in the western part of the Peninsular Ranges Province, rocks crop out on both sides of both branches of the San Andreas thick sections of lowei (?) and middle rocks, consisting of fault in the - region, but do not appear argillaceous, volcanic, and graywacke assemblages, crop out south of the Banning fault. The southern boundary of Precambrian (Larsen, 1948; Schwarcz, 1969, p. 6). The Bedford Canyon rocks is interrupted at and near the San Jacinto fault, with about 30 Formation of the Peninsular Ranges; (at least in part Callovian) and to 40 km of right-lateral separation (Allen, 1957; Sharp, 1968). One the Santa Monica Slate of the have been of the most distinctive units within the Precambrian is tentatively correlated across the Malibu Coast-Cucamonga fault syenite-anorthosite and related rocks exposed in the San Gabriel zone (Hoots, 1931; Woodford, 1960; Imlay, 1963). Exposures of Mountains (Higgs, 1954), Mojave Desert (Crowell and Walker, these two units are separated, however, by extensive Tertiary and 1962, p. 262-264), (Crowell and Walker, 1962; Quaternary cover in the Los Angeles Basin. Silver, 1971), and Sonora, Mexico (Merriam, 1972). Steeply dipping east-trending structures, primarily foliation and The eastern Transverse Ranges contain known and presumed late layering, prevail in pre-batholithic rocks throughout most of the Paleozoic quartzite and marble in relative abundance. The largest, Transverse Ranges Province (Fig. 4). These structures are in addition least deformed, and least recrystallized masses occur in the eastern to the prevalence of elongate east-trending roc.c units ranging in age part of the north flank of the San Bernardino Mountains (Woodford from Precambrian to late Paleozoic. In the Alamo Mountain and and Harriss, 1928; Dibblee, 1964; Guillou, 1953; Richmond, Frazier Park areas, many kilometers northwest of Los Angeles, 1960), where a Mississippian age has been documented b> fossils. At structural data indicate a northwest: trend for pre-(P) rocks the south edge of the Paleozoic area, a quartz-pebble basal (Carman, 1964), suggesting that they lie north of the Transverse

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Figure 2. Major faults in and adjacent to the Transverse Ranges Province, California.

20 40 SO eo KILOMETERS

0 10 20 30 40 90 HILCii

Ranges. But, from the Lake Hughes area on the northwest and the In southern California, these rocks, in numerous individual plutons, Santa Monica Mountains on the southwest (Fig. 1), east-trending range from granite to gabbro, with quartz monzonite, granodiorite, structures predominate eastward through the San Gabriel and quartz diorite predominating. In general, the relative amount of Mountains to the San Andreas and San Jacinto faults. Deviations mafic rock increases regularly across the batholith from the Mojave from this orientation occur primarily in the vicinity of some granitic Desert in the northeast to the Pacific Coast in the southwest (Fig. 5). bodies and the Vincent thrust. Lack of gabbro of Mesozoic age is a distinctive feature of the Similarly, in the San Bernardino Mountains, easterly trends Transverse Ranges Province. predominate. They pass into a northwest-.rending structural grain in the northern part of the San Bernardino Mountains (Richmond, Petrochemistry 1960; Dibblee, 1964) and into a similarly oriented grain eastward Major- and minor-element chemistry for the rocks shown in and southeastward. Figure 5 are presented in Table 1. These values are arranged by North of the Transverse Ranges Province, structures are major fault-bounded blocks. The most obvious chemical changes predominantly northwest-trending, though those along the Garlock fault are coincident with the generally east-northeast strike of the fault. Within the Mojave Desert Province, scattered data show diverse structural orientations (Fig. 4). In the Peninsular Ranges Province, a northwest-trending structural grain is markedly consistent (Fig. 4). This grain has been the same from pre-batholithic time to the present (for example, Larsen, 1948, p. 119; Gastil and others, 1974). Local structural deviations appear to be the result of the emplacement of plutons of the southern California—peninsular batholith.

BATHOLITHIC ROCKS Distribution Batholithic rocks of late Mesozoic age crop out in a remarkably straight, elongate pattern from southern Baja California, through southern California, into the Sierra Nevada. Granitic rocks of PRECAMBRIAN similar age also occur in the Coast Ranges Province (Salinia block), Figure 3. Distribution of rocks of known or inferred Precambrian age, southern west of the San Andreas fault, as far north as Point Reyes (see Fig. 8). California.

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TABLE 1. CHEMISTRY AND SPECIFIC GRAVITY CF BATHOL ITHIC ROCKS stress conditions, but these ideas may have to be modified in light of the Pb dates. Whatever the origin of rocks of group two (abnormal age), it is Structural Weight percent elemert clear from present evidence that they form a belt through the Q. 1. n block Na Hg Al S1 P K Ca TI Fe t/1 Ol Transverse Ranges across the San Andreas fault system. In contrast, ages of batholithic rocks in the Peninsular Ranges Province are San X 2.89 0.56 8.29 32.40 0.02 3.47 2.08 0.33 1.79 2.672 139 Bernardino 8 0.41 0.56 0.79 2.10 0.03 0.71 0.89 0.12 1.30 0.043 remarkably consistent by both dating methods and are significantly older by 10 to 45 m.y. (Silver, 1971). Little San X 2.86 0.71 8.15 32.42 3.17 1.84 0.27 2.05 2.693 25 Bernardino 8 0.28 0.60 0.56 1.48 0.60 0.92 0.18 1.46 0.090 POST-BATHOLITHIC ROCKS San X 2.88 0.91 8.62 31.15 2.57 2.43 0.34 2.91 2.737 49 Gabriel 8 0.22 0.56 0.61 2.26 0.67 1.09 0.13 1.34 0.051 East trends predominate among the post-batholithic structures San X 2.70 0.87 8.67 30.97 0.06 2.29 2.78 0.44 2.76 2.729 101 Jacinto B 0.23 0.39 0.56 1.76 0.02 0.67 0.81 0.13 0.81 0.041 of the Transverse Ranges, although northwest-trending structures prevail both to the north and south (Fig. 9). The most prominent Perris X 2.66 1.34 8.50 30.60 0.06 1 .71 3.53 0.35 3.25 2.759 128 8 0.57 1.10 0.86 2.87 0.02 0.82 1 .90 0.15 1.33 0.074 east-trending feature is the Ventura-Soledad basin, which is roughly paralleled by many subsidiary trends and structures. These Santa X 2.70 1.50 8.35 30.23 0.04 1.58 3.73 0.34 3.65 2.769 97 east-trending basins developed by late Oligocene time, with Ana e 0.49 1.37 1.26 4.20 0.02 0.92 2.53 0.18 1 .85 0.099 concomitant deformation (Oakeshott, 1958; Edwards, 1971). In the note: n = number of localities; i = mean; 8 = stcndard deviation Santa Ynez Mountains area, Dibblee (1950, p. 61 and cross sections) found that rocks (Espada and Jalama Formations) were deformed prior to the deposition of Eocene rocks (Anita Formation are marked by a general and regular increase in Mg, Ca, and Fe, and and Matilija Sandstone). In the northern Santa Ynez Mountains, an decrease in Si and K toward the continental margin from the Oligocene deformation produced east-trending folds in the Gaviota northeast to the southwest (Baird and othsrs, 1970). The over-all Formation (upper Eocene-lower Oligocene?) and older formations trend of the chemical zones is northwest; however, north of the (Dibblee, 1950, p. 62). Crowell (1971) noted east-west patterns in Malibu Coast—Cucamonga, Banning, and Pinto Mountain faults, Cretaceous and Eocene times as well. Hoots (1931) showed repeated both chemical and specific gravity patterns are east-trending (Figs. 6 deformation of Cretaceous and younger rocks about an and 7). Patterns in each fault-bounded block of both the Transverse east-trending axis in the eastern Santa Monica Mountains. In the and Peninsular Ranges provinces show a marked tendency toward northern Los Angeles Basin, the trends of most conglomerate and internal consistency, with siliceous cores and basic margins. We other lithological units are east-west to northeast (Woodford and have interpreted this feature to suggest a close causal relation others, 1946, Fig. 2). The conglomerates were derived from the between batholithic emplacement and the structural framework of north and northeast (Bellemin, 1940). Miocene volcanic rocks southern California (Baird and others, 1970). extend across the Cucamonga fault (Shelton, 1955). Pre- shorelines north of the Transverse Ranges Province Structure clearly trended northwest; their orientation in the Transverse Structures within the Mesozoic granitic rocks essentially parallel Ranges Province is ambiguous, but depositional areas of an those of the prebatholithic rocks but appear somewhat more limited east-west attitude occur in parts of the area. Yerkes and Campbell in areal distribution due to lack of recorded measurements (Fig. 4). (1971) stated that north-trending shorelines prevailed from the Late No data have been collected for the Lake Hughes and Santa Monica Cretaceous to early Miocene time in the Santa Monica Mountains. Mountains areas of the western Transverse Ranges Province, as well To the northwest, however, in the central Santa Ynez Mountains, as for much of the Mojave Desert Province. Plutons within the Dibblee (1966, p. 43) concluded that the lower Miocene Vaqueros Transverse Ranges Province tend to have their long dimension Sandstone and Rincon Shale were deposited in a sea with an preferentially oriented in an eastward direction, while those in the east-trending shoreline. North of the Santa Ynez Mountains, in the Peninsular Ranges Province are mostly either concentric or oriented Pine Mountain area, Givens (1969, p. 54) interpreted Eocene in a northwest direction, regardless of their mode of emplacement sediments as having been deposited on the northern margin of an (Larsen, 1948; Gastil and others, 1974). east-trending embayment. Among the most significant of all the Transverse Ranges features are the east-trending structures Ages developed in Miocene to Pleistocene rocks. In Figure 8, the age distributions of late Mesozoic plutonic rocks Structural trends are varied just south of the Transverse Ranges. in California are shown in three separate patterns following the The dominant northwest trend is shown by the axis of the central designations of Evernden and Kistler (1970, Fig. 1): first, those faulted anticline of the (Fig. 9), but the middle batholithic rocks belonging to their sequence of intrusive epochs Miocene-Pliocene strata of the (eastern part of the (here called "normal"); second, those batholithic rocks of abnormal Basin) show trends ranging from west- age character; and third, those rocks for which specific age northwest to north-south, and the axes of folds in the information is lacking. We have modified the information of Kistler (northeastern part of the greater Los Angeles Basin) trend and Evernden to include in the second group rocks of the San northeast. For the first 30 km south of the Malibu Bernardino Mountains north and east of all branches of the San Coast—Cucamonga fault zone, marine Late Cretaceous to early Andreas fault on the basis of new radiometric dates obtained by Miocene strata are unknown, surface or subsurface. Far to the west, Silver (1971, and 1971, personal commun.). Knowledge of the real the 1,100 m of quartz-feldspar-biotite Eocene sandstone on San distributions of rocks of abnormal age characteristics must await Nicolas Island (Vedder and Norris, 1963) trend N. 62 W.; these study of rocks in the third group. The nature of this age abnormality rocks lie beyond the northwest-trending Catalina Schist of Santa is not well understood. Evernden and K:.stler (1970) noted dis- Catalina Island. cordant K-Ar biotite and hornblende dates and abnormally young East of the San Jacinto fault and south of the Pinto Mountain and average dates for the Transverse Ranges rocks. Subsequently, Silver Blue Cut faults (Hope, 1971), most trends in the very young (1971) also found significantly younger ages (75 to 90 m.y., (Pliocene and Pleistocene) marine and continental beds roughly by the Pb method) in upper Mesozoic rocks of the Transverse parallel the nearest fault, but in and east of Borrego Valley, in the Ranges Province. Evernden and Kistler believed that the retention of Peninsular Ranges Province, similar strata trend northeast, argon in these rocks was affected by deep burial and (or) unusual perpendicular to the San Jacinto fault.

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STRUCTURAL DEVELOPMENT THROUGH TIME NORMAL AGE We have alluded to repeated deformations which have produced ABNORMAL AGE structures in harmony with the trends existing within each province. Here we shall further discuss these events areally through time. Almost all writers agree that in southwestern California the foliation and related structures of the pre-batholithic rocks must have originated prior to, or synchronously with, the emplacement of the commonly undeformed Cretaceous batholithic rocks. Possible exceptions are the Pelona and related schists. The age of these schists has been considered pre-batholithic (Precambrian or early Paleozoic, Miller, 1934, p. 63) or, more recently, postbatholithic (Ehlig, 1958, 1968). North of the Garlock fault, in the , a gabbro body emplaced within schist deflects foliation from an otherwise clearly northwest trend (Wiese, 1950). Mapping of metamorphic rocks on the Mojave Desert indicates a pre- batholithic development of structures that are, at least in part, northwest trending (Dibblee, 1964; Bowen and Ver Planck, 1965). In the northwestern Transverse Ranges, mapping in the Lebec area (Crowell, 1952) and Lockwood Valley area (Carman, 1964) indicates a discordance between batholithic and pre-batholithic rocks, with granitic dikes crosscutting northwest-striking foliation in Precambrian augen gneiss in the Lockwood Valley area (Carman, 1964, p. 13). Within the San Gabriel Mountains, Cretaceous granitic rocks have been emplaced both concordant to east-trending foliation (for example, Morton, 1973) and as discordant bodies clearly crosscutting pre-existing east-striking foliation and layering (for example, Baird, 1956). On the north slope of the San Bernardino Figure 8. Distributions of batholithic rocks with no rmal and abnormal radiometric Mountains, a prebatholithic age has been shown for northwest- age dates. Modified after Evernden and Kistler (1970). See text for discussion. trending foliation and folds in Paleozoic rocks (Guillou, 1953; Richmond, 1960). Richmond (1960, p. 12-13) further indicates

STRIKE OF BEDS AXIAL TRENDS

Figure 9. Strike of beds and trend of fold axes within-post-batholithic rocks of southern California.

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that the Carboniferous Furnace Formation was folded prior to the Abundant data support repeated development of east-trending intrusion of Triassic( ?) volcanic rocks. On the south slope of the San structures in the western Transverse Ranges c uring, and subsequent Bernardino Mountains, northeast of all branches of the San Andreas to, middle Miocene time (Winterer and Durham, 1962; Campbell fault, east-striking Precambrian and Paleozoic metasedimentary and others, 1966; Dickinson and Lowe, ' 966). During middle rocks are interlayered with Cretaceous granitic rock. Discordance Miocene time, ancestral San Gabriel Mountains rose and shed between northwest-oriented foliation in Precambrian gneiss and coarse debris into the Los Angeles Basin (Woodford and others, Cretaceous(P) quartz monzonite occurs in the northeasternmost San 1946; Yerkes and others, 1965). The left-lateral movement on the Bernardino Mountains (Dibblee, 1967a). Similar discordances exist Malibu Coast—Cucamonga fault zone postulated by Yerkes and between east-trending structures and granitic rocks in the central Campbell (1971) must have occurred before middle Miocene time. part of the San Bernardino Mountains (Dibblee. 1964). The middle Miocene Glendora Volcanics (Shelton, 1955) and a late Granitic rocks east of the Little San Bernardino Mountains deflect Miocene sand lens (Eschner and Scribner, 1973) can be correlated northwest-striking, prebatholithic foliation in rocks of the Hexie directly across the fault line. East-trending basins (Ventura-Soledad) Mountains (Hope, 1966) and crosscut similarly oriented foliation in and structures were especially pronounced during the Pliocene the Coxcomb Mountains (Greene, 1967). Within the northern (Vedder and others, 1969; Yeats, 1965). During the Pleistocene and Peninsular Ranges, numerous cases have been cited of northwesterly Holocene, east-trending structural deformation (folding and trending structures of prebatholithic age (Jenney, 1968; Larsen, faulting) throughout the Transverse Ranges seemingly reached its 1948; Morton, 1969; Schwarcz, 1969). Thus, prebatholithic apex, with the formation of the present-day topography. structures show a marked agreement with the present-day shape and Deformation of Cenozoic rocks of the Mojave Desert Province orientation of the natural provinces, and compel us to believe that has produced nortnwest-trending structures (Dibblee, 1967b; the east-trending transverse structures had their origins some time Rogers, 1967). Just south of the Transverse Ranges, northwest- prior to the emplacement of the Cretaceous granitic rocks. trending structures developed from the Late Cretaceous through Within the Cretaceous granitic rocks, primary planar structures Cenozoic time, with the Los Angeles Basin providing the best record (for example, igneous foliation and mineral layering) which have of the periods of deformation, principally from the middle Miocene been recorded show a marked gross parallelism to the pre- to the present (Yerkes and others, 1965). East of the Santa Ana batholithic structures (Dibblee, 1968; Larsen, 1948). In southern Mountains, lack of pre-Pliocene sediments precludes establishment California, most of the individual plutons have their long map of a complete history of Cenozoic d eformation. Pliocene-Pleistocene dimension parallel to the provincial structural grain, regardlsss of nonmarine sediments were deposited in predominantly northwest- whether the pluton locally disrupted this grain (for example, oriented basins, and subsequent deformation of the basins appears Morton, 1969), was passively and concordantly emplaced (for to be the result of movement associated with the northwest-striking example, Jenney, 1968), or was passively and discordantly faults. emplaced (Morton, unpub. mapping). Most pluton elongatiors and Thus, the geologic record of southern California indicates clearly intraplutonic structures in Baja California trend northwest or the initiation of transverse structures prior to the emplacement of north-northwest, though a few are circular (Gastil and others, Cretaceous granitic rocks. The record further indicates that similarly 1974). Thus the structural patterns developed prior to the oriented structures were formed repeatedly through time, as were emplacement of the batholith were, in general, reinforced by the northwest-trending structures in the areas north and south of the emplacement of the batholith (but intrusion also produced local Transverse Ranges Province. deflections in the regional grain) and are reflected in the distribution of chemistry within the batholith. Although postbatholithic DISCUSSION deformations have generally intensified the earlier structures, they The revolution in g;eology that began with Mason (1958) and the have been of a nonpenetrative nature. discov ery of frequent magnetic reversals (Cox and others, 1964) arid Within the Transverse Ranges, the earliest east-tre iding culminated in the new global tectonics (for example, Morgan, 1968) postbatholithic events in crystalline rocks produced a series of has been extended to explain the continental structural evolution of cataclasites within granitic and granulitic rocks in the southeast- western (Atwater, 1970). In this concept, the San ernmost San Gabriel Mountains (Alf, 1948; Hsu, 1955). The Andreas fault is a plate boundary of the transform variety. Hill relations, temporal and genetic, of this east-striking cataclastic belt (1971a) has criticized this interpretation of the San Andreas fault and cataclastic rocks associated with the west- to northwest-striking and stimulated useful discussions (Matthews, 1972; Dickinson and Vincent thrust are uncertain. Ehlig (1968) considered the cataclastic others, 1972; Atwater, 1972; and Paschall, 1972) which, in our deformation associated with the Vincent thrust to have been Late opinion, have more clearly delineated how the new global tectonics Cretaceous and postbatholithic. Similarly, a north- to northwest- has been applied to the San Andreas fault than any earlier writing striking belt of cataclastic rocks extending from the eastern San and also have provided clear statements of what was known or Jacinto Mountains to the Borrego area, Peninsular Ranges, has been inferred in 1972 about the movement history of the fault or fault tentatively dated as Eocene or older (Sharp, 1968, p. 292). Possibly system. We believe that Hill's criticisms and the subsequent this belt is correlative with the cataclasites of the San Gabriel discussions, taken with some other papers to be cited below, form a Mountains, but the relation is most uncertain. Crowell (1971) stated basis for discussing the significance of the orientation of the that an east-trending fracture pattern is suggested for the Transverse Ranges Province across the San Andreas fault zone in Cretaceous, Paleocene, and Eocene sediments of the Transverse southern California. Ranges. Atwater (1972) has re-emphasized that, according to the Winterer and Durham (1962, p. 334) considered that the Ventura plate-tectonic model, all motion between the Pacific and North Basin was a depositional area throughout the Tertiary. Variations in American plates may not be taken jp along a single plane of failure thickness in the Eocene to lower Miocene continental rocks in the with right-lateral slip (the San Andreas fault, sensu stricto) western Transverse Ranges may represent east-trending structural throughout Cenozoic time. We recognize as a consequence, irregularities. Sediments were deposited in a subsiding Ve:itura therefore, that our conclusions concerning the tectonic evolution in Basin during late Oligocene time (Edwards, 1971, p. 115). During the vicinity of the Transverse Ranges Province may have little or no early Miocene time, a narrow east-trending elongate trough had bearing on the validity of her concept. On the scale of western North developed and migrated southward and later northward from near America, we are discussing a local complication; on the scale of Santa Barbara (Winterer and Durham, 1962, p. 334; Edwards, southern California, a major feature which has yet to be adequately 1971). explained. Atwater (1972, p. 388) is of the opinion that relative

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motions between plates must be worked out with vector diagrams or right-lateral strike-slip faults, each more than 200 km long, might deduced "by careful work with paper and sc .ssors." We believe good have developed, extending from the original southeast end to the geologic maps, petrological and structural studies, and many more present east end, and from the original northwest end to the present radiometric dates will be needed before the Transverse Ranges west end. The original east end of the block would have rotated from Province ceases to be a basketful of enigmas. We next examine these the vicinity of San Diego to its present position. The whole of the San enigmas. Bernardino Mountains would be allochthonous. Other centers of A majority of writers (Hill, 1972, p. 384, is a major exception) rotation would involve different, but related, original positions. In believe that the Transverse Ranges divide the San Andreas fault one possible scheme, rotation about an axis at the present west end system into two parts with different movement histories. North of of the province would produce a great circle overlap of about 370 the Transverse Ranges, recent studies (for example, Turner and km at the east end of the block, with a sweep across an area that is others, 1970; Huffman, 1970; Nilsen and Clarke, 1972) have added now largely ocean, and an arcuate boundary fault more than 400 km to a growing and convincing set of evidence for 305 km of long. Analogously, rotation about an axis at the east end of the right-lateral slip, post-Oligocene. In the same period, south of the province would have been from a position wholly northeast of the Transverse Ranges, Crowell (1962) finds only 260 km of offset on San Andreas fault and would imply the deposition of marine Late the combined San Gabriel and San Andreas faults. Dickinson and Cretaceous and Cenozoic strata in the place now occupied by the others (1972) think that this figure can be increased to nearly 305 Mojave Desert and Tehachapi Mountains. km, and they conclude there is no problem. But, those who accept Actually, the Mojave Desert contains Neogene continental beds the Atwater model (with the Gulf of California opening in the past 4 and shows no relics of the marine rock types of the central and m.y.) and who propose that the resulting hundreds of kilometers of western Transverse Ranges and no signs of the great rotation. In right-lateral slip were taken up on the San Andreas fault zone, are in fact, few suggestions of rotation about any center exist anywhere, conflict with much evidence. Woodburne and Golz (1971, 1972) though the change in strike of the San Andreas fault suggests the find no more than 25 km of post-middle Pliocene displacement in possibility of flexure. The San Bernardino Mountains have probably Cajon Pass on the San Andreas fault. Sharp and Silver (1971) find 42 been thrust 2 or 3 km onto the Mojave Desert block, judging from km of post-Pliocene offset on the combined Punchbowl—San data recorded by Woodford and Harriss (1928). In the west-central Andreas faults; and Dibblee (1968) ar.d Sharp (1967) find a part of the Transverse Ranges Province, north-south compression maximum offset of 25 km on the San Jacin :o fault, another strand of with thrust faulting has occurred, but it reaches a maximum only the San Andreas system. Even adding these values (whether or not slightly west of the center of the province (compare Jennings and warranted), to obtain about 90 km, leaves more than 200 km Strand, 1969). We can see, on published maps, no evidence of either unexplained. The missing 200 km cannot be found on other faults of an eastern or a western arcuate boundary fault. Rotation about the the San Andreas system (for example, Elsinore, Newport- present center of the province, whether the block involved included Inglewood), as shown by Jahns (1969, Fig. 3). Further, the evidence its whole 400 km length or only that part west of the San Andreas of Woodburne and Golz, Sharp and Silver, Dibblee, and Sharp does fault, would juxtapose the Precambrian rocks and other distinctive not seem compatible in any way with the picture of rapidly rocks, radiometric ages, and structures of the eastern Transverse accelerating movement on the northern part of the San Andreas fault Ranges and the equally distinctive Mesozoic rocks and other in the last 10 m.y. (Dickinson and others, 1972, Fig. 2). features of the Peninsular Ranges, retaining as an original feature the To solve these dilemmas of post-Oligocene movements of the San contrast between the north and south sides of the Malibu Andreas fault system, upward relief, thrusting, or rotation of Coast—Cucamonga fault zone. northwest-trending rock belts and structures to an east strike A crucial, and currently insoluble, problem in attempting to apply forming the Transverse Ranges have been suggested in oral large-scale rotation to explain the Transverse Ranges is the timing of discussions of a paper by Baird and others (1970), by Carter and the event. Proposers of this idea seem to believe that rotational Silver (1971), by Anderson (1971), and by a reviewer of an earlier deformation was (and is?) related to the opening of the Gulf of version of this paper. That uplift has occurred is undoubted, and that California, beginning 4 m.y. ago, and caused by the northwestward thrust faulting has played and continues to play (U.S. Geol. Survey, sliding of the Peninsular Ranges (Anderson, 1971), including Baja 1971) a major role in the structural development of the Transverse California. Evidence cited earlier in this paper indicates that the Ranges seems beyond controversy. However, a history that includes Transverse Ranges were a high, rugged land mass shedding coarse gross rotation of crustal blocks seems to us improbable at best. Any debris into the Los Angeles Basin at least as early as middle Miocene such rotation must include the western as well as the eastern parts of time, about 15 m.y. ago. Other evidence cited suggests development the Transverse Ranges Province. It must take into account the of east-trending depositional basins and source areas within the present east-west strike of the very complete and enormously thick Transverse Ranges Province in Oligocene time (Vasquez Formation, Late Cretaceous and Cenozoic section in the west. The N. 70° W. Soledad Basin) and perhaps as early as the Late Cretaceous. strike of the San Andreas fault at the north edge of the San Gabriel Pre-Miocene slip on the San Andreas north and south of the and associated ranges is only part of the problem. Transverse Ranges Province was grossly different (Dickinson and If the rotation of the province was less than 90°, it would be about others, 1972, p. 382). Ross (1972, p. 37) found no evidence to 55° counterclockwise. Under compressional north-south stresses, support the idea that the San Andreas fault (sensu stricto) juxtaposes one might assume rotation about a nearly vertical central axis, tilted significantly different basement rocks in the Transverse Ranges (see slightly to produce maximum elevation at the northeast and also Dibblee, 1971). Suppe (1970) proposed an ancestral or maximum depression at the southwest. The major axis of the proto—San Andreas fault for southern California, which may Transverse Ranges Province, now east-west, is about 400 km long. coincide with the present Newport-Inglewood zone, at which At the midpoint, the width is about 80 km. An approximate central oceanic and continental basement terrains are perhaps in contact. point is about 2 km south of Saugus and 45 km northwest of He suggested that this proto—San Andreas fault has been offset tens downtown Los Angeles, in the eastern part of the Los Angeles sheet of kilometers in a left-lateral sense at the southern boundary of the of the state geological map (Jennings and Strand, 1969). Rotation of Transverse Ranges Province. Campbell and Yerkes (1971) also 55° counterclockwise would have crowded this block against the recognized a dual history for the San Andreas fault. Their model blocks to the northeast and southwest, perhaps with overthrusting involved a piecemeal attachment of continental North America to northeastward east of the center and overthrusting southwestward the . During its first stages, which must have ended at west of the center. Maximum great circle overlap of about 190 km least 10 m.y. ago, the San Andreas fault did not extend south of the would then occur at the extreme eastern and western ends. Arcuate Transverse Ranges. The model provides for a much older transverse

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range than the rotational scheme discussed above, but only for that the rather gentle and very slow vertical and horizontal deformation portion west of the San Andreas fault. In our opinion, the of anticlinal basement highs, synclinal basement lows, and Campbell-Yerkes (1971) model is a step toward the resolution ;>f the superjacent strata that has affected the Los Angeles Basin from apparent conflict between Atwater's (1970) concepts and known mid-Miocene time to i:he present? How is this deformation related to geologic facts about southern California geology. It does not, strike-slip displacements of tens of kilometers on some faults durin g however, address the problems of Catalina Schist correlation and the same period? How can the apparent aggregate displacements of Miocene-Holocene tectonic evolution. T. L. Wright and others perhaps 50 km for most rocks and structures in the Transverse (1973, p. 813) suggested "6-8 miles of sinistral Miocene-Pliocene Ranges be reconciled with proposed offsets of 260 or 305 km to the offset" on the south frontal fault zone of the Transverse Ranges, but southeast for individual rocks units in the Transverse and Tehachapi such movement seems incompatible with the elongation north- Ranges? How, during all these disturbances, have three strips of south, across the fault, of the vertically displaced Glendora early basement (San Gabriel—San Bernardino Mountains, Sierra Pelona, middle Miocene volcanics (Shelton, 1955) and a late Miocene sand and Sawtooth Mountains) in the Transversa Ranges maintained lens (Eschner and Scribner, 1973). east-west alignment? How has another, much longer basement strip, extending south-southeast for 1,400 km, from the Transverse CONCLUSIONS Ranges to the tip of the peninsula o f Baja California, and composed As a local complication in the scheme of global tectonics, the of an exceptionally uniform rock assemblage, maintained continuity Transverse Ranges Province remains a severe problem for any throughout the opening of the Gulf of California and the relentless interpretation of southern California structural evolution. In relative displacements of the American and Pacific plates? attempting to resolve detailed interplate movements, any proposed tectonic framework must operate to maintain the structural integrity ACKNOWLEDGMENTS of the Transverse Ranges (Burk and Moores, 1968, p. 369). The T. W. Dibblee, Jr.. M. L. Hill, M. O. Woodburne, and R. F. dynamic explanation of the orientation of these ranges must await Yerkes read an earlier version of this paper. Their numerous the development of a detailed genetic theory of plate movements. criticisms, we hope, have been partially answered in the present One major structural-petrochemical boundary in southern version of the paper. E. E. Welday was a major contributor to the California is that between oceanic and continental crust, perhaps at petrochemistry. the Newport-Inglewood zone. This boundary is terminated to the northwest against a second major boundary which follows the REFERENCES CITED Malibu Coast—Cucamonga-Banning fault zone, and the Salton Alf, R. M., 1948, A mylonite belt in the southeastern San Gabriel Mountains, Trough to the southeast (Fig. 3). This second boundary separates California: Geol. Scic. America Bull., v. 59, p. 1101-1119. basement with known and presumed Precambrian from that Allen, C. R., 1957, San ¿Andreas fault zone in San Gorgonio Pass, southern apparently devoid of rocks older than late Paleozoic. It coincides California: Geol. Soc. 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Printed in U.S.A.

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