FINAL TECHNICAL REPORT

PALEOSEISMIC AND STRUCTURAL INVESTIGATIONS TO DETERMINE LATE QUATERNARY SLIP RATE FOR THE CHINO FAULT, SOUTHEASTERN LOS ANGELES BASIN, CALIFORNIA

U.S. Geological Survey National Earthquake Hazards Reduction Program External Grant Award Number 04HQGR0107

Recipient Earth Consultants International 1642 E.. 4th Street, Santa Ana, CA 92701 Phone: (714) 544-5321; Fax: (714) 494-4930 Web: www.earthconsultants.com

Principal Investigators Christopher Madden and Robert Yeats [email protected] and [email protected]

Program Element III Research on earthquake occurrence, physics and effects

Key Words Paleoseismology, Quaternary Fault Behavior, Earthquake Recurrence, Segment Interaction, Fault Interaction

October 2008

Research supported by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award number (Recipient, insert award number). The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.

TABLE OF CONTENTS ABSTRACT...... 3 1.0 INTRODUCTION ...... 5 2.0 BACKGROUND...... 5 2.1 Regional Bedrock Stratigraphy...... 5 2.2 Regional Bedrock Structure...... 13 2.3 Displacement History of the Chino Fault ...... 19 2.4 Seismicity...... 25 3.0 PALEOSEISMIC INVESTIGATIONS AT MCMASTERS CANYON...... 26 3.1 Geomorphology of McMasters Canyon Area...... 26 3.2 Methodology ...... 27 3.3 Canyon Trenches...... 32 3.3.1 Bedrock and depositional units exposed in canyon bottom...... 32 3.3.2 High angle faulting within the canyon ...... 34 3.4 Hillslope Trenches...... 35 3.4.1 Bedrock and depositional units exposed along rangefront ...... 35 3.4.2 Low angle faulting...... 36 3.5 Summary of Faulting at McMasters Canyon ...... 36 4.0 DISCUSSION ...... 37 4.1 Timing of Holocene Earthquakes on the Chino Fault ...... 37 4.2 Slip Partitioning along a structural complexity on the southern Chino fault...... 37 4.3 Slip budget between the Elsinore fault and the Puente Hills...... 38 5.0 CONCLUSIONS...... 40 APPENDIX 1: REFERENCES...... 43 APPENDIX 2: WELLS USED IN CROSS SECTIONS IN FIGURE 3 ...... 50 APPENDIX 3: PLATES...... 51

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ABSTRACT

The Chino fault crops out low on the northeast flank of the Chino Hills, an uplift separate from the larger Puente Hills uplift to the west. The structure includes, in addition to the fault, the parallel Mahala anticline and Ridge syncline to the west, west of which Aliso Canyon separates Chino Hills drainage from southwest-flowing Puente Hills drainage. It also includes the west-northwest- striking Slaughter Canyon anticline to the east, which appears to divert the course of Chino Creek. Although clearly active in the late Quaternary, the seismic hazard of the Chino fault is poorly constrained. This paleoseismic and structural investigation provides new constraints on the rupture history and slip rate for the Chino fault, and the interaction of this structure with the Elsinore and Whittier faults. Trenches across the Chino fault on an undeveloped parcel between Prado Dam and Slaughter Canyon exposed a 30-40 m-wide zone of distributed high- angle bedrock faults coincident with the mapped trace of the Chino fault, and a significant, unmapped low-angle fault zone cutting Pleistocene fan/terrace deposits upslope of the mapped trace. The high-angle faults do not cut a debris flow with a calibrated AMS 14C age of ~3.2-3.5 ka. The development of a strong argillic soil on unfaulted colluvium underlying the debris flow, suggests the fault has not ruptured since at least the mid-Holocene. When compared to a maximum age of ~11 ka for the last rupture from a trench site at the north end of the Chino fault, our findings suggest the most recent event occurred in the early to mid-Holocene. The low-angle fault zone has ruptured since the Pleistocene, but the recency of rupture cannot be constrained at the site. A left-bend or step in the Chino fault immediately north of the paleoseismic site may cause localized uplift and partitioning of slip across the project area. In this model, the diffuse, high-angle fault zone would accommodate lateral slip and the low angle dip-slip fault would accommodate dip slip motion.

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A new review of well data for this study suggests that no stratigraphic evidence of coeval Chino faulting is found in Miocene bedrock. However, the strike of the fault is parallel to that of normal-separation faults in the Prado-Corona oil field east of the fault, suggesting that it is a reactivated Miocene normal fault related to uplift of the Perris Block to the east. Maximum dip separation of the contact between the Yorba and Sycamore Canyon formations is 700 m near the southeastern end of the Chino Hills, which converts to a maximum dip separation of 800 m based on a fault dip of 60º. Dip separation decreases to zero at Los Serranos, at the north end of the Chino Hills, where the Mahala anticline and Ridge syncline also die out. Maximum shortening of this contact is 400 m, a reflection of folding. Bedrock structure from Los Serranos northward is a northeast-dipping homocline. We conclude that the right-slip rate on the Chino fault does not exceed 0.5 mm/yr, and that the fault may originally been vertical, deformed to a reverse-separation fault later in its history. Although the Chino fault may account for some of the decrease in slip rate between the Elsinore fault at Glen Ivy Canyon and the Whittier fault at Santa Ana Canyon, displacement on other structures is required, including the Coyote and La Habra folds south of the Whittier fault, the Arena Blanca syncline and Scully Hill fault north of the fault, and uplift of the northern end of the Santa Ana Mountains.

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1.0 INTRODUCTION

The goal of this investigation is to provide better constraints on the slip rate, earthquake history and structure of the Chino fault. To accomplish this goal, we excavated 6 trenches within a fault-deflected canyon along the last undeveloped portion of the Chino Hills. In this report, we first review the previous work that serves as the foundation for the current project, then describe our paleoseismic methods and results. We close with a discussion on the implications of our results for the activity and structure of the Chino fault, and the interaction of the Chino fault with the nearby Whittier and Elsinore faults.

2.0 BACKGROUND

2.1 Regional Bedrock Stratigraphy

The northwest corner of the Peninsular Ranges is underlain by the late Mesozoic Peninsular Ranges batholith (Figure 1, which shows batholithic and pre- batholithic rocks together). The batholith is largely in the subsurface in the area of intersection of the Elsinore, Whittier, and Chino faults. Granitic rocks comprise the basement of the central and northern Puente Hills (Yeats, 2004) and, to the east, the Chino Basin and Perris Block north of 33˚ 50’ N. This is in contrast to exposures in the Santa Ana Mountains immediately to the south, where pre- batholithic rocks predominate (Schoellhamer et al., 1981; Gray et al., 2002). In the Santa Fe Minerals Government 165-1 well (Well 35 on Figure 2 and cross section F-F’ on Figure 3), granitic rocks are overlain by Late Cretaceous strata, including the nonmarine Trabuco Formation and the Baker Canyon Conglomerate Member and Holz Shale Member of the Ladd Formation (Lang, 1978). Lang (1978, his fig. 3) showed that the overlying Williams Formation, widespread in the Santa Ana Mountains to the south (Schoellhamer et al., 1981) is overlapped northward by Paleocene strata that rest directly on Holz Shale in the Government 165-1 well. The southern subsurface boundary of granitic rocks beneath Upper Cretaceous

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Ridge MAHALA Mahala syncline OIL FIELD anticline CORONA Aliso 22 23 18 FREEWAY Chino LOS Canyon 24 1 3 RF 25 Creek 26 27 28 4 RF SERRANOS 5 E A Ty Ty E’ 0 Tsc,Tf A’ 0 Ty Tsc Tsc, Tf ? 2 Tsq Tlv Ty Ty Tt Tlv Ts Tlv Tt gr Tlv Tsa Ts K Mahala Tt Anticline CORONA FREEWAY 6 7 8 Chino 9 RF Creek MAHALA B Tsc OIL FIELD 0 B’ 30 Tsc, 29 31 32 RF Ty Tf 33 34 35 36 Tsq, Ty Ty Tlv undif. F F’ granite 0 Tlv Tsc Tf 2 0 1 Ty Tsc Ty, Tsq undif. Tsq, Tsc basement? Tlv Ty Tsq (Hunter zone) KILOMETERS undif. Tsi,Tsa Mahala Slaughter Tsq Kh anticline anticline Ty Tsq Kbc 10 11 12 RF CORONA Chino FREEWAY Creek 13 14 Kt C Tsc Tsc Q C’ granite 0 Q Quaternary undifferentiated Tsc,Tf Ty Ty granite Tf Fernando Formation, Pliocene PRADO-CORONA Ty Ty CORONA OIL FIELD FWY.37 38 39 40 41 42 43 Tsc Sycamore Canyon Formation G’ Tt Tlv M G 0 Ty Yorba member Tsc Tf i Tsc Ridge MAHALA Tsc Aliso Mahala o Tsq Puente Ty Canyon syncline OIL FIELD anticline Soquel member ss, undif. 16 18 c Formation (Mio) 15 17 19 20 21 Ty Ts Tsq e Tlv La Vida member Tsq grano-diorite D Tsc D’ n Tlv Tt K 0 e Tt Topanga Formation Ts Tsc Tsc 35 Ty Ts (proj.) Ty 0 1 2 Sespe Formation, Oligocene Ty Ty Langstaff Tt Tsa Tsq Tsa Santiago Formation, Eocene PRADO-CORONA zone KILOMETERS OIL FIELD Ts Fault in CORONA K RR cut 45 4647 Upper zone Tsi Silverado Formation, Paleocene Tsc 44 48 Willis zone H H’ C 0 r Tf e Kh Holz Shale Tsc t Ty a Tlv Kbc Baker Canyon Formation Tsq c Ts Ts e Tsa o K u Kt Trabuco Formation Tsi s Figure 3. Cross sections across Chino fault with well control. Wells identified in Table 1, and located on Figure 2. granitic basement RF, range front. Note the absence of the Chino fault in cross section A-A‘ at north end of study area. See Appendix 2 for wells used in cross sections. NEHRP Report 04HQGR0107 8 strata strikes approximately east-southeast across the Puente Hills between the Morton and Sons Rowland Estates well in Hacienda Heights and Jurassic metavolcanic rocks in the hanging wall of the Whittier fault at Brea-Olinda Oil Field (Yerkes, 1972; Yeats, 2004) extending east across the Chino fault (but not considering possible horizontal offset across that fault) to the Chino Basin, where the contact is south of the Government 165-1 well and north of pre-batholithic exposures in the Santa Ana Mountains on the south side of the Santa Ana River (Schoellhamer et al., 1981; Gray et al., 2002). The Paleocene Silverado Formation is overlapped northward by the Eocene Santiago Formation, which is itself overlapped by the “Sespe” Formation farther north (McCulloh et al., 2000, their fig. 8). The Paleogene marine-nonmarine facies boundary, of which these overlaps are a part, is convex westward in map view, striking north in the northwestern Santa Ana Mountains and northeast closer to the Whittier fault (McCulloh et al., 2000). McCulloh et al. (2000) found a right-lateral offset of this facies boundary of 8-9 km across the Whittier fault, but did not have enough well control to establish evidence for lateral offset of Paleogene facies boundaries across the Chino fault. The well control in Paleogene strata is sparse enough that a kilometer or two of strike slip is not prohibited by their data. Paleogene strata are overlain unconformably by the nonmarine “Sespe” Formation. Schoellhamer et al. (1981) mapped the nonmarine Sespe and marine Vaqueros formations together as one, undifferentiated formation, but McCulloh et al. (2001) found that marine Vaqueros strata are unknown north of the Santa Ana River. For this reason, the strata are referred to here as “Sespe” rather than “Sespe- Vaqueros,” even though part of our study area is south of the Santa Ana River. The name “Sespe” is in quotes because the strata are younger than the Eocene-early Miocene Sespe Formation at its type locality in the Ventura Basin. “Sespe” vertebrate fossils in the Santa Ana Mountains are referred to the early Hemingfordian Vertebrate Stage and to the paleomagnetic Chron C5Cr to C5Er (17-19 Ma) by Prothero and Donohoo (2001). The “Sespe” contains clasts of Mountain Meadows Dacite dated at 27.6 ± 0.4 Ma, indicating uplift and erosion of

9 NEHRP Report 04HQGR0107 that unit prior to “Sespe” deposition (McCulloh et al., 2001). The “Sespe” overlaps Paleogene strata to rest directly on granitic rocks in Shell Puente Core Hole 4 (McCulloh et al., 2000; well 2, Figures 2 and 3). The “Sespe” is itself overlain by the Topanga Formation of middle Miocene age based on molluscan fossils (Durham and Yerkes, 1964) and on foraminifers of the Luisian and Relizian stages of Kleinpell (1938). This is the same as the Topanga Group of Wright (1991) and McCulloh et al. (2001), which includes the Glendora Volcanics with ages ranging from 15.08 to 17.2 Ma (McCulloh et al., 2002). Volcanic rocks are absent in the easternmost Puente Hills and adjacent Chino Basin. Topanga strata are exposed only in the vicinity of Santa Ana Canyon (Schoellhamer et al., 1981), although they are widespread in the subsurface. McCulloh et al. (2001, their fig. 6) drew a Topanga shoreline east of and parallel to the Chino fault, building on a suggestion by Woodford et al. (1946). The eastward overlap of the Topanga by the overlying Puente Formation is illustrated in cross section C-C’ and E’E’ (Figure 3). The Puente Formation was named by Eldridge and Arnold (1907) for a clastic sequence of late Miocene age in the Puente Hills. They divided the Puente into a lower shale, middle sandstone, and upper shale, which were named by Schoellhamer et al. (1954) the La Vida, Soquel, and Yorba Members, respectively, a usage followed by Gray (1961) and Durham and Yerkes (1964). Dibblee (2001a, b) dropped the name Puente Formation and mapped these three units as members of the Monterey Formation, a usage we do not follow here. The La Vida Member is lower Mohnian in the biostratigraphy of Kleinpell (1938) and Division E of Wissler (1943, 1958). The Soquel and Yorba members are upper Mohnian as defined by Kleinpell (1938) and Division D and C, respectively, of Wissler (1943, 1958). The Soquel is mainly deep-water sandstone, a turbidite fan probably derived from an ancestral San Gabriel Mountains to the north (Woodford et al., 1946; Critelli et al., 1995). The Soquel lenses out eastward toward the Perris Block, forming stratigraphic traps for the Langstaff and Willis zones of the Mahala Oil Field (Castro, 1975; Olson, 1977; Cross Sections D-D’ and E-E’, Figure 3) and the Hunter

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zone of the Prado-Corona Oil Field (Gaede, 1969; Cross Section G-G’, Figure 3). The Yorba Member, based on a surface section southwest of Los Serranos (Figure 2; Cross Section A-A’, Figure 3), is siltstone with a subordinate amount of fine-grained sandstone (Durham and Yerkes, 1964, B19-B20). The La Vida Member rests directly on granite in well 9, cross section B-B’, and the Yorba Member rests on granite in well 14 in cross section C-C’ and in well 28 in cross section E-E’, Figure 3. Undifferentiated Puente Formation overlies pre-batholithic rocks southeast of Corona (Gray, 1961). This shows that the Puente Hills, Chino Hills, and the northern Santa Ana Mountains were receiving marine sediments at this time, whereas the Perris Block east of the Chino Hills and the San Gabriel Mountains north of the Puente Hills were above sea level, shedding detritus into the marine basin. In the northwestern Puente Hills, Daviess and Woodford (1949) found coarse clastic Miocene strata overlying the Yorba Member that they named the Sycamore Canyon Member of the Puente Formation. The Sycamore Canyon Member contains microfossils of the Delmontian Stage of Kleinpell (1938) and Divisions A and B of Wissler (1943, 1958), although upper Mohnian microfossils have also been found in the type section. Dibblee (2001a, b) raised the Sycamore Canyon to formation status, but we follow the older usage of Daviess and Woodford (1949) and Durham and Yerkes (1964). The Sycamore Canyon is found in the footwall of the Whittier fault in both the western and eastern Puente Hills (Bjorklund and Burke, 2002), but in the hanging wall, surface exposures of Sycamore Canyon in the eastern Puente Hills are separated from those in the western Puente Hills by older strata. In the southeastern Puente Hills and in the Chino Hills, post-Yorba strata were correlated to the Sycamore Canyon by Krueger (1943) and Durham and Yerkes (1964). The Sycamore Canyon Member in the southeastern Puente Hills consists of a basal thick-bedded to massive medium- to coarse-grained sandstone with lesser amounts of siltstone and conglomerate (Durham and Yerkes, 1964, B21). This is the bedrock at the trench site. The contact with the Yorba Member is marked by the upward transition from Yorba siltstone

11 NEHRP Report 04HQGR0107 and shale to coarser clastic strata of the Sycamore Canyon Member. Upper Mohnian and Delmontian faunas are found in the Sycamore Canyon of the southeastern Puente Hills (Durham and Yerkes, 1964). The uppermost exposures in the Ridge and Arena Blanca synclines in the southeastern Puente Hills (located in Figure 2) might be Pliocene, a possibility recognized by Woodford et al. (1946), Gray (1961), and Castro (1975), but Durham and Yerkes (1964) and Dibblee (2001b).arbitrarily mapped the entire section as Sycamore Canyon. The Pliocene Fernando Formation is known mainly from the subsurface of the Chino Basin and from the La Habra syncline south of the Whittier fault (Durham and Yerkes, 1964; Yerkes, 1972; Bjorklund and Burke, 2002). In the Prado-Corona Oil Field, the Fernando is coarse grained and is divided into lower and upper members, but the relatively shallow-water facies precludes a correlation of these members to the deep-water Repetto and Pico Members of the Fernando Formation in the La Habra syncline and farther west and south in the Los Angeles Basin. East of the Chino fault, Gray (1961) and Gray et al. (2002) described shale and siltstone with minor amounts of sandstone and conglomerate containing Pliocene foraminifers; southeast of Corona, the exposures are sandstone and conglomerate with a few siltstone interbeds. An ash bed on the north flank of the Peralta Hills on the south side of the Santa Ana River (located by Schoellhamer et al., 1981, their p. D55) was correlated to the Nomlaki Tuff by A.M. Sarna-Wojcicki and T.H. McCulloh (pers. comm., 2000) with an age of 3.4 ± 0.3 Ma. The same ash bed was found by these geologists in the Repetto Member of the Fernando Formation in the Santa Fe Springs Oil Field southwest of the Puente Hills (Myers et al., 2003). Another ash bed interbedded with conglomerate and sandstone and buttressed against granitic basement in the Norco area in the Chino Basin was correlated to the Ash of Taylor Canyon with an age of 2.8 Ma (A.M. Sarna- Wojcicki, pers. comm. to D. M. Morton, 1990; Morton and Gray, 2002). Unlike the Los Angeles and San Gabriel basins to the west, the Chino Basin does not contain a thick sequence of nonmarine Pleistocene strata (California Division of Water Resources, 1970; French, 1972), although Morton and Gray

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(2002) described as Pleistocene moderately-indurated sandstone and conglomerate in the Norco area. The coarse clastic sequence is best exposed in the Coyote Hills south of the Whittier fault, where it consists of the marine San Pedro Formation and the nonmarine Coyote Hills and La Habra formations (Yerkes, 1972; Tan et al., 1984). The upper part of the San Pedro Formation yielded a mollusk from which a Sr age estimate of 1.4 ± 0.3 Ma was obtained (Powell and Stevens, 2000). The Coyote Hills Formation, along with older formations, contains far-derived crystalline clasts, whereas the overlying La Habra Formation is dominated by locally-derived clasts from the Puente Formation (Yerkes, 1972), indicating the timing of uplift and erosion of the Puente Hills and other areas underlain by marine Miocene strata.

2.2 Regional Bedrock Structure

The Puente Hills are a broad uplift, triangular shaped in plan, with the San Jose Hills on the north, the Whittier fault on the south, and the Chino fault on the east (Figure 1). The Puente Hills probably owe their elevation to the restraining bend of the right-lateral, north-dipping Whittier reverse-separation fault that crops out near the southern edge of the hills. The hills end on the west at Whittier Narrows where the Whittier fault bends to the right (from northwestward to north- northwestward) into the East Montebello fault (Yeats, 2004), and they end on the east at Santa Ana Narrows where the fault bends to the right (southeastward) into the Elsinore fault (Figure 1). The Chino fault also has reverse separation and also lies low on the northeast flank of the Chino Hills, but uplift of the Chino Hills may not have the same origin as uplift of the Puente Hills. Where the Puente Formation is underlain by granitic rocks in the Puente Hills, it is broadly deformed, but in the southeastern Puente Hills along and north of the Santa Ana River, the strata comprise an east-west fold belt that includes the Arena Blanca syncline and the Scully Hill and Aliso faults (Figure 2). This fold belt extends westward across the Whittier fault into the Los Angeles Basin as the Coyote

13 NEHRP Report 04HQGR0107 fold belt (Myers et al., 2003), which may be the surface expression of the Puente Hills blind thrust (Shaw et al., 2002; Figure 1). The location of the Quaternary Whittier fault is influenced by Miocene structure including volcanic rocks in an extensional basin along the Whittier fault expressed in isopachs of the La Vida Member of the Puente Formation (Bjorklund et al., 2002). Similarly, the Chino fault is parallel to the Prado-Corona normal fault, which formed prior to deposition of the Sycamore Canyon Member (Figure 2; Figure 3, cross section G-G’) and the Sardco fault, which predated deposition of the Fernando Formation (Figure 2; cross sections F-F’ and G’G’, Figure 2). These southwest-side down normal faults are part of the western margin of the Perris block of Woodford et al. (1971), who found evidence for deposition of strata with Clarendonian (late Miocene-Pliocene) vertebrate fossils on its oldest and highest erosion surface. The Chino Basin is a Miocene half-graben in which Miocene strata are buttressed against Peninsular Ranges granitic rocks such that individual formations thicken westward and wedge out eastward, as shown in several cross sections in Figure 3. The Central Avenue fault of Woodford et al. (1944), was proposed on the basis of a possible ground-water barrier that was, however, not confirmed by subsequent studies (California Department of Water Resources, 1970; French, 1972). The “Central Avenue fault” of McCulloh et al. (2000, p. 1168), the “Chino Hingeline fault” of Wright (1991, p. 114), and the Topanga shoreline of Woodford et al. (1946) appear to be controlled by Miocene normal faulting, especially the Prado-Corona fault of Gaede (1969). The modern faults apparently follow older zones of crustal weakness, although the modern stress field has changed. Treiman (2002a; Figure 4) found linear vegetation and tonal lineaments near the hypothesized trace of the Central Avenue fault, and a slight stream-incised scarp on 1953 air photos near the intersection of Edison and Ramona Avenue northeast of Los Serranos. He concluded that none of these features showed evidence of Holocene activity; some of the lineations may be cultural in origin. The area,

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15 NEHRP Report 04HQGR0107 however, has higher seismicity than does the Chino fault (Hauksson, 1990; see further discussion below). Although Luyendyk (1991) showed the Peninsular Ranges as tectonically unrotated, Teissere and Beck (1973) demonstrated that the Peninsular Ranges are rotated ~26˚ clockwise from their expected Cretaceous direction. In addition, Prothero and Lopez (2001) showed even greater clockwise rotation of upper Paleocene strata in the Santa Ana Mountains. The Chino Hills are physiographically the eastern end of the Puente Hills, but structurally they are a separate feature (Figure 5). The geomorphic boundary is Aliso Canyon, cut by a south-flowing stream that has east-flowing tributaries flowing into it from the Puente Hills to the west and southwest-flowing short streams entering from the Chino Hills to the east (Figures 2 and 5). The eastern Puente Hills are underlain by an east-dipping homoclinal sequence of the Soquel, Yorba, and Sycamore Canyon members of the Puente Formation (Durham and Yerkes, 1964; Cross Section A-A’; Figure 3). East of Aliso Canyon, these strata are folded into the Ridge syncline and Mahala anticline, both of which trend north- northwest, subparallel to the Chino fault (Figures 2, 6). The Chino fault system can be said to consist of the Chino fault itself, the active Mahala anticline to the west, which accounts for uplift of the Chino Hills, and the Ridge syncline, which separates the Chino Hills from the Puente Hills. The fault and associated folds postdate deposition of the Sycamore Canyon Member. The fault disappears northward into alluvium near Los Serranos and may die out (Figures 2 and 3), although the fault might continue northwest at the base of the hills north of Los Serranos based on a weak topographic lineament on the digital elevation model. The fold dies out, too, so that the east-dipping homocline continues eastward into the Chino Basin across the northward projection of the Chino Hills (cross section A-A’, Figures 3, 6). On the south side, in contrast, the Chino fault is traced beneath the floodplain of the Santa Ana River into Wardlaw Wash (Heath et al., 1982; Treiman, 2002a). Farther south, the Chino fault joins the Elsinore fault (Gray, 1961; Gray et al., 2002; Treiman, 2002a, b; Figure 4).

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2.3 Displacement History of the Chino Fault

Miocene strata show no evidence of growth relative to the Chino fault or its associated folds, although these strata are buttressed against the Perris Block to the east. The Fernando Formation also shows no effect of uplift of the adjacent Chino Hills. It is probable that the Fernando Formation formerly covered the Chino Hills. The youngest strata mapped as Sycamore Canyon by Durham and Yerkes (1964) and Dibblee (2001b) may, in fact, be correlated to the Fernando Formation. The Chino fault is an oblique-slip fault. Vertical separation of the Sycamore Canyon-Yorba contact along the fault is as much as 450 m (Figures 3, 6, and 7). However, the true vertical separation should take into account the vertical difference between the contact on the crest of the Mahala anticline and in the flat- floored Chino Basin to the east, as shown in cross sections B-B’ through E-E’ (Figure 3). This vertical separation is as high as 700 m (Figure 7). If a dip of 60˚ is assumed for the Chino fault, a maximum dip separation of 800 m is calculated. This must diminish to near zero in a distance of 6 km between the Mahala Oil Field and Los Serranos. Although we are confident that there is strike slip along the fault, based on offset streams across the northern part of the fault outcrop, we were unable to obtain piercing-point evidence in the Puente Formation of the strike-slip component. The shortening component at right angles to the Chino fault can be determined from cross sections in Figure 3, using the Yorba-Sycamore Canyon contact and measuring from the axis of the Ridge syncline east to the point where this contact is flat-lying in the Chino Basin (Figure 6). Shortening is 400 m in cross section D-D’ and 370 m in cross section E-E’. The shortening is 500 m in cross section A-A’ of Durham and Yerkes (1964), which extends cross section C-C’ of Figure 3 across the Ridge syncline to the west. This crossing includes the Slaughter anticline and Slaughter syncline east of the Chino fault. The shortening is 500 m in cross section F-F’ of Durham and Yerkes (1964), which crosses the Mahala

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117 42.5'W 33 57.5'N 117 40'E 33 55'E a.

500 Los Range Slaughter Canyon Folds Abacherli area Corona Range Santa Ana Serranos front Mahala oil field Freeway front River Prado-Corona N 40 W Oil field S 40 E S 40 E 0 (sea level) meters

Arena Blanca Syncline 500

0 2000 4000 6000 8000 10000 1000 1000 b. 1000 3000 5000 7000 9000 11000 meters

500 meters

Vertical exaggeration 2:1

Figure 7. a) Altitude of base of Sycamore Canyon Member of Puente Formation along crest of Malhala anticline southwest of Chino fault and in Chino basin northeast of fault. This is used to determine change in vertical separation across Chino fault at crustal depths since it includes fault separation and folding on the northeast flank of Malhala anticline and southwest flank of Chino Basin syncline. Vertical exaggeration 2:1. b) Vertical separation of base of Sycamore Canyon Member across Chino fault based on a. Low values north of Slaughter Canyon may indicate fault dies out: compare with cross section B-B‘ with C-C’ in Figure 3.

20 NEHRP Report 04HQGR0107 anticline 600 m southeast of cross section C-C’ in Figure 3. However, this cross section is constructed on the assumption that steep surface dips measured in Yorba siltstone in the crest of the Mahala anticline indicate steeper dips at the Yorba- Sycamore Canyon contact at depth, hence greater shortening. The anticline is not constrained at depth in this cross section by subsurface well data, whereas cross sections C-C’ and D-D’ in Figure 3 on both sides of the Durham and Yerkes cross section, with subsurface control, show gentler anticlinal dips at this contact, hence less shortening (Figure 6). South of cross section E-E’ of Figure 3, the Ridge syncline is succeeded southward by east-west structures, including the Arena Blanca syncline, and only a minimum shortening of 200 m is measured in cross section F-F’ of Figure 3.

2.4.1 Late Quaternary Activity The late Quaternary history is constrained by trench excavations across the fault combined with study of tectonic geomorphic features (summarized by Treiman, 2002a). Walls and Gath (2001, modified by Treiman, 2002b) salvage- logged a trench near the northwest end of the Chino fault in the Chino Hills, about 50 m northwest of cross section B-B’ (WG, Figure 4). The trench placed Sycamore Canyon Member in fault contact with alluvium and buried soils (Figure 8). The main strand of the fault, with a vertical dip, offsets an actively-developing soil to within one meter of the surface. The base of the soil profile, with a calibrated radiocarbon age of 10,925 +/-275 yrs BP, overlies but is not offset by a secondary fault. Three soil boundaries are warped and vertically offset 15-25 cm, west side up. Underlying the active soil, a contact between a colluvial unit and a pebbly sandy clay loam radiocarbon dated at 13,250 ± 950 yrs BP (calibrated) strikes east and is orthogonal to the fault. Matching apparent dips of this contact along the fault surface requires 4.2-5.6 meters of right-lateral strike slip from at least two events in the past 14,200 yrs and an average slip rate of 0.3-0.5 mm/yr on the Chino fault (Walls and Gath, 2001, modified by Treiman, 2002a). This slip rate determination is from that part of the fault where total vertical separation of the

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Yorba-Sycamore Canyon contact is 300 m, in contrast to 600-700 m farther southeast, suggesting that the slip rate farther southeast might be higher. Offset ridge lines and deflected and beheaded drainages in this area show right-lateral deflections of 25 to 100 m (Figure 9); stream captures might mask larger deflections of 400-500 m (Walls and Gath, 2001). Right steps along the fault trace coincide with embayments in drainage basins (Walls and Gath, 2001), suggesting transtensional faulting in contrast with the long-term transpressional displacement of the Yorba-Sycamore Canyon contact. Alternatively, the right steps might be controlled by faulting parallel to steeply-dipping bedding in the Sycamore Canyon Member adjacent to and drag folded along the fault (Treiman, 2002a). Southeast of the Chino Hills, the fault is apparent as vegetation lineaments on aerial photos taken prior to construction of Prado Dam and as a low, northeast- facing scarp 3-6 m high near the 91 Riverside Freeway east of the Prado Dam area and across the Corona fan (Weber, 1977; Smith, 1977; Heath et al., 1982). Weber (1977) estimated the age of the older fan deposits to be 40-400 kyr. Near Prado Dam, older sand, gravel, and silt are overlain by reddish gravelly deposits that encroach from the southeast (Heath et al., 1982). Several trenches were excavated across the fault, showing a zone of faulting as much as 100 m wide with reverse separation, down to the northeast. Analysis of test borings and trench excavations by Heath et al. (1982, location HJL, Figure 4) showed that the bedrock-Quaternary contact had a vertical separation of as much as 17 m (60 feet). The vertical separation of the base of a discontinuous fine-grained sand and silt deposit (their

Qo1) is about 8 m (25 feet). Assuming the age of these alluvial deposits to be 125- 200 kyr, Heath et al. (1982) estimated the vertical separation rate to be 0.06 mm/yr near Prado Dam, with an unknown rate of strike slip assumed to be comparable to the vertical separation rate, with separation at the surface both by faulting and warping. The offset sediments were not dated, and the trenches provided no information about relations to Holocene or latest Pleistocene deposits. Because of these uncertainties, we assume that the vertical separation rate is a minimum rate.

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Farther southeast, near the intersection of the Chino fault with the Elsinore fault, the floor or Hagador Canyon (between Mabey Canyon and Tin Mine Canyon) appears to be uplifted between the Elsinore (Main Street) fault on the southwest and an arcuate thrust fault on the northeast, inferred by Treiman (2002a, b) to be the southeast continuation of the Chino fault. Similar soils cover the surface in both the hanging wall and footwall sides of this thrust fault (Treiman, 2002a, b; Gray et al., 2002). Two different elevated surfaces contain soils with estimated ages of 100 and 200 kyr, respectively. A younger fluvial surface (older Hagador Canyon floor) is offset vertically 5.5 m and horizontally 15-30 m along the scarp that follows Chase Drive (Treiman, 2002b). Treiman (2002b) estimated the age of this inset surface to be latest Pleistocene to Holocene, although this age is not confirmed by radiocarbon dating. If the age of this surface is 10 kyr, near the beginning of the Holocene, the vertical component of slip rate would be 0.55 mm/yr, and the strike- slip component would be 1.5-3 mm/yr. Although the most recent offset on this fault is very likely Holocene, the age of the surface itself might be 20,000 to 30,000 yr. The ratio of vertical to horizontal slip is 1:3 to 1:6.

2.4 Seismicity

Seismicity along the Chino fault is relatively low. Hauksson and Jones

(1991) described an earthquake of ML 4.3 on February 16, 1989 with a fault-plane solution consistent with right-lateral strike slip on a fault parallel to the Chino fault. This earthquake and its aftershocks are located 2 km southwest of the northwest projection of the Chino fault in the Chino Hills, consistent with a fault of moderate southwest dip. However, the 1989 earthquake is located northwest of where the Chino fault dies out at and near the surface. This earthquake might be part of the northeast-striking Yorba Linda seismicity trend of Hauksson (1990) that has no surface expression. An analogous earthquake might be the ML 4.8 Yorba Linda earthquake of September 3, 2002, which had a fault-plane solution consistent with right-lateral movement on the Whittier fault but was revealed to have a northeast

25 NEHRP Report 04HQGR0107 strike based on its aftershock distribution (Hauksson et al., 2002). Also in line with the Yorba trend was an earthquake of M 3.9 at 13.8 km depth on December 14, 2001, mapped 3 km west of the mapped northern end of the Chino fault near the city of Chino Hills (Treiman, 2002a). A Mw 5.4 earthquake on July 29, 2008 occurred southwest of the Chino fault and approximately 4 kilometers north of the Yorba Linda earthquake. The moment tensor showed a mixture of thrust and left-lateral strike-slip faulting on a plane striking 43 degrees east of north, with a dip of 58 degrees and on a plane striking 291 degrees with a dip of 59 degrees. (http://earthquake.usgs.gov/eqcenter/eqinthenews/2008/ci14383980/#summary). These orientations are similar to the Whittier fault, and Yorba Linda trend, respectively. The aftershock pattern for this earthquake, however, was too diffuse to determine the orientation of the causative fault. A zone of seismicity 8-16 km east of and parallel to the Chino fault between latitude 33˚ 45’and 33˚ 55’ N does not have any geological expression, although it might be related to faulting at the west edge of the Perris Block.

3.0 PALEOSEISMIC INVESTIGATIONS AT MCMASTERS CANYON

3.1 Geomorphology of McMasters Canyon Area

The paleoseismic site for this investigation lies in an unnamed drainage near the southern end of the Chino Hills that we call McMasters Canyon (MC on Figure 4). In this area, a steep northeast-facing bedrock escarpment transitions abruptly to a series of low foothills that extend approximately 600 m northeast of the escarpment (Figure 10). The foothills comprise a dissected low-relief surface that is capped by older alluvium (Heath et al., 1982) and underlain by sandstone and siltstone of the Puente Formation. Canyons draining the east flank of the Chino Hills transition from actively incising v-shaped drainages in the steeper hills to the west, to aggrading flat-bottomed drainages in the foothills to the east. Landslides are common in the Chino Hills, and a large active slide occurs 120 m northwest of

26 NEHRP Report 04HQGR0107 the study site (Figure 10). A possible older dissected slide also occurs directly upslope of the site. The Chino fault is geomorphically expressed through the study area by slope breaks and saddles at the abrupt transition between the escarpment and the foothills. The fault strikes northwest through the study site and steps left (southwest) approximately 300 m northwest of McMasters Canyon (Figure 10) (Treiman, 2002a). Drainages in the vicinity of the trench site exhibit evidence of right lateral separation along the fault. The drainage immediately northwest of McMasters Canyon appears to be deflected at least 50 m along the fault (Figure 10). The next drainage to the north ends abruptly against the escarpment, suggesting that it has been beheaded and possibly offset a minimum of 140 m from a large unnamed canyon to the north (Figure 10). Due to the complexity of the fault trace through the left step in this area, the offset could be as much as 275 meters if the behead channel is connected to where the unnamed canyon leaves the escarpment. McMasters Canyon does not appear to be significantly offset, but may be deflected up to 10 m along the fault. Several geomorphic indicators constrain the location of the Chino fault across the study area. A prominent saddle and slope break between the escarpment and foothills marks the Chino fault on the northwest wall of McMasters Canyon (Figure 11). Approximately 30 m upslope of the saddle, a subtle break in slope may mark another fault trace. A subtle break in slope on the interfluve immediately south of McMasters Canyon is coincident with an 8 to 10 m deflection of the canyon wall. A more prominent slope break occurs 20 m upslope of the southern interfluve.

3.2 Methodology

We excavated four trenches near subsurface cross sections E-E’ (Figure 2) within McMasters Canyon and two trenches on slopes south of the canyon for this

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29 NEHRP Report 04HQGR0107 investigation (Figure 12). The trenches were excavated using a large trackhoe and were oriented to intersect faults inferred from the geomorphic features discussed above and as mapped by the California Geological Survey (Treiman, 2001a). Our trenching strategy was to first excavate fault-perpendicular trenches along the canyon margins to locate the main strands of the Chino fault and then to excavate fault-parallel trenches on either side of the fault to expose offset channels that could be used to constrain fault slip. We placed trench 1 along the northwest wall of McMasters canyon, below the prominent saddle expressed in the interfluve. We extended the trench approximately 30 m up-canyon of the saddle to capture any low angle fault strands dipping toward the escarpment. The purpose of trench 1 was to locate the main strand of the Chino fault in bedrock exposed in the canyon wall on the northwest wall of the trench and to trace the fault to channel deposits exposed in the southeast wall of the trench. Trench 2 was excavated closer to the center of the canyon. The purpose of this trench was to expose older channel deposits adjacent to the west end of trench 1, which had exposed faulted bedrock mantled only by young soil and colluvium. This colluvium was too young to constrain the activity of the bedrock faults. We excavated trenches 3 and 4 to determine whether the apparent deflection of the southeast wall of McMasters Canyon is fault-controlled. The trenches were oriented to reveal whether the contact between bedrock and overlying alluvial and colluvial units was faulted at the deflection. The presence of only minor bedrock faulting in the canyon trenches led us to excavate trench 5 to search for more significant faulting across a prominent break in slope in the escarpment south of McMasters Canyon (Figures 11 and 12). This slope break lies upslope and 20 m southwest of the mapped trace of the Chino fault (Treiman, 2002a) and the geomorphic features targeted by the canyon trenches. Trench 6 was excavated down a deeply incised rill that crossed the projection of a prominent fault zone exposed in trench 5. The goal of this trench

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N

Trench 1

Trench 4

Figure 12. Map showing trench locations, Late Quaternary alluvium and fault locations across the McMasters Canyon study site. Oriented tic marks show the strike of fault strands measured in trenches. Fault dips are shown on Plates 1 and 2. Topographic lines from the San Bernardino County Department of Planning. 31 NEHRP Report 04HQGR0107 was to search for offset Holocene channel deposits within the rill that could be used to determine the slip rate and slip per event for the Chino fault. Based on the findings from the fault-perpendicular trenches, no fault-parallel trenches were excavated for this investigation. This is because the main strand of the Chino fault exposed on the hillslope in trench 5 intersected McMasters Canyon in an area of active incision, where channel deposits were not preserved across the fault. In trench 6 the fault did not disturb the thin mantle of colluvium and soil overlying the fault. Furthermore, bedrock faults exposed in McMasters Canyon did not cut overlying latest Holocene deposits. In other words, our investigations showed that the last event on the Chino fault predated the mid-to late Holocene deposits preserved at the site. All trench walls were scraped to remove loose material from the excavation and to reveal stratigraphic and structural relations. Level lines with 0.5 m delineations were placed in all the trenches except trench 5, where a 0.5 by 1 m string grid was erected on both walls. The southern walls of all the canyon trenches and trench 6 were logged at a scale of 1:20. Both walls of trench 5 were photo- logged. Eight charcoal samples were collected from channel deposits in trenches 1 and 2. The four samples from trench 1 were collected from the same stratigraphic unit. The stratigraphically lowest sample in trench 1 was sent to Beta Analytic for accelerator mass spectrometer (AMS) radiocarbon dating. The charcoal samples in trench 2 were too small to be dated.

3.3 Canyon Trenches

3.3.1 Bedrock and depositional units exposed in canyon bottom

Trenches 1 and 2 exposed fine-grained facies of the Sycamore Member of the Puente Formation (Tsc) mantled by hillslope colluvium (Qc) derived from the northwest wall of the canyon (refer to Plate 1 for all discussions related to trenches 1 through 4 in McMasters Canyon). The colluvium is overlain by packages of

32 NEHRP Report 04HQGR0107 alluvial canyon fill (Qya1-3) and debris flow deposits (Qd). Bedrock is typically lower on the southeast wall of trenches 1 and 2 because the canyon deepens in that direction. At the northeast end of trench 1, the southeast wall is benched and extends several meters further into the canyon and exposing deeper alluvium than the same wall at the southwest end of the trench. Trench 2 is also closer to the center of the channel and exposes deep alluvium. In trenches 1 and 2, unit Tsc consists of massive to well-bedded sandstone and siltstone with local beds of granitic conglomerate. Bedding orientations range from N30W, 20-26SE near the northeast end of trench 1 to N65W, 42SW near the middle of the trench, with dips locally as steep as 72SW in the northeast half of trench 2. Even though dips in Cross Section E-e’ (Figure 3) and the structural contour map (Figure 6) are right side up. We interpret the southwest dips as overturned, produce by fault drag. Tsc is exposed throughout the base of trench 1, except for an 8 m wide section near the northeast end of the trench. In trench 2 Tsc is exposed near the base of all but the southwest-most end of the northwest wall and the northeast half of the southeast wall. Qc consists of porous, massive clayey sand and silt with scattered fine gravel. Qc overlies Tsc bedrock for most of the length of trench 1 and all of trench 2. Strong prismatic peds, abundant clay films on ped faces and reddish brown color define a strong paleosol on this unit in the northeast end of trench 1. The only area where Qc was not observed is where a 6 m wide zone of extensive burrowing near the southwest end of trench 1 has extended the A soil horizon to the top of bedrock. We infer an early to mid Holocene age for this deposit based on the development of a strong argillic soil horizon at the top of this unit. The debris flow deposit, Qd, exposed in the northeast half of trench 1 consists of medium to fine grained granitic gravel in a clay matrix. A sharp contact along the base of this unit suggests that it scoured into the underlying Qc deposit. This deposit is not exposed in any of the other trenches, suggesting that it is a small remnant deposit. An AMS 14C date constrains the radiocarbon age of Qd to 3273- 3470 years BP (calibrated).

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Three distinctive alluvial deposits are exposed in sections of the trenches extending furthest toward the center of the canyon. In trench 1, very loose, gravelly silts and sands, Qya1, fill small channels incised into more indurated and finer deposits of Qya2. In trench 1, Qya2 is incised into Qc. In trench 2, Qya2 is locally incised into an even more indurated alluvial unit, Qya3. The lack of soil development and friability of these units suggest that they are Late Holocene to modern in age. Trenches 3 and 4 on the southeast side of the canyon exposed primarily Tsc overlain by Qc. One exception is the southwest end of trench 4, where alluvium (Qal) is underlain by weathered sandstone of Tsc and overlain by Qc. Qal consists of well-indurated, well bedded sand and gravel on a low bedrock strath terrace. The texture and induration of Qal do not resemble the young channel units Qya1- Qya3 and likely represent an earlier period of filling of the canyon. Based on the induration of the Qal, and its position above the mid-to-late Holocene channel fill, we infer a late Pleistocene to early Holocene age to this deposit.

3.3.2 High angle faulting within the canyon

Trenches 1 and 2 exposed a broad zone of diffuse northwest-striking high- angle bedrock faulting and fracturing in the Puente Formation. In trench 1, clusters of faults were centered at approximately 12 m, 30 m, 41 m and 46 m from the northeast end of the trench. A zone of intense fracturing occurs between meters 28 Strikes of the faults near meter 12 range from N22W to N10E with dips of 79SW and 85SE respectively. These faults generally parallel the strike of the bedrock, but locally cut across more shallowly dipping beds. The faults produce minor vertical separations of bedding contacts within the bedrock. Near meter 30, a fault with a thin seam of gouge dies upward within the bedrock. Three faults near meter 4 have an average orientation of N28W, 80SW. Apparent vertical separations of thin bedrock strata range from 10 to 20 cm across these faults. Lastly, a cluster of faults between meters 45 and 48 mark the most concentrated zone of faulting in the

34 NEHRP Report 04HQGR0107 trench. Most of the faults in this zone strike N15-28W and dip 80NE to vertical, respectively. A distinctive sandstone bed in the Tsc exhibits up to 1 m of dip-slip separation across one of the faults. The northeastern-most fault of the zone juxtaposes bedded siltstone against massive siltstone. The lack of significant separation of bedrock beds across these faults suggests that net slip for each fault is low. None of the faults in trench 1 extend upward into the overlying colluvium. Because of the lack of colluvial deposits between meters 37 and 44, intense bioturbation of A soil horizons, and the possibility that the irregularity of the top of bedrock could mask faulting of surficial deposits in this portion of the trench, we excavated trench 2 parallel to this section and deeper in the canyon. Bedrock faults in trench 2 all die upward into a weathered zone near the top of the bedrock. Furthermore, the top of the bedrock/colluvium contact in trench 2 is smooth, without any sudden breaks. Thus faulting in trenches 1 and 2 predates the deposition of the colluvium, which in turn predates the deposition of the overlying Qd unit, dated at 3273-3470 years BP (calibrated). Trenches 3 and 4 contained no bedrock faulting. A low-angle, northeast dipping “fault” cuts the older alluvium, but not the overlying colluvium in trench 3, however. This “fault” dips into the canyon suggesting that it is an old slope failure.

3.4 Hillslope Trenches

3.4.1 Bedrock and depositional units exposed along rangefront

Massive conglomerates of the Sycamore Canyon Member of the Puente Formation (Tsc) are exposed at the southwest end of trenches 5 and 6 (Plate 2). In trench 6, Tsc conglomerate is faulted against siltstones from the base of the Tsc section. In trench 5 Tsc is faulted against older alluvium (Qoa) consisting of crudely to well-bedded clayey sand and silt with rare gravel beds. These alluvial deposits are strongly indurated and have reddish-brown colors. The presence of these deposits on the top of interfluves adjacent to McMasters Canyon suggests that

35 NEHRP Report 04HQGR0107 they are late Pleistocene terrace or fan deposits. In trench 6, colluvium derived from Qoa is in depositional contact with Tcs. A thin A soil horizon is developed into the top of the alluvium, colluvium and bedrock in trenches 5 and 6. This soil thickens in the vicinity of the fault zones exposed in the trenches.

3.4.2 Low angle faulting

A well-developed, low angle fault zone was exposed in the southwest end of trenches 5 and 6. In trench 5, this fault zone is 5 m wide and places Tsc over and against Qoa. Fault strands range from horizontal to gently southwest-dipping. Tsc is pulverized along the fault zone. In Qoa, three low-angle faults in trench 5 are stacked vertically, one on top of another. Steep northeast-dipping fractures occur in Qoa between these faults. Near the surface, an A soil horizon is developed more deeply into the Tsc on the southwest side of the fault than in the Qoa on the northeast side of the fault. This could be due to to deeper soil development in the pulverized Tsc. There is no evidence that the A horizon in trench 5 has been faulted. In trench 6, the fault zone juxtaposes Tsc conglomerate against Tsc siltstone. Here the fault zone is 6 m wide. There is no evidence that any faults cut the A horizon in trench 6.

3.5 Summary of Faulting at McMasters Canyon

Two discrete zones of faulting were exposed in the study area. A 30-40 m wide zone of diffuse high angle bedrock faulting was exposed within McMasters Canyon. These faults do not cut mid-to-late Holocene deposits that overlie the bedrock. A discrete zone of low angle, southwest dipping faults was exposed upslope of the high-angle canyon fault zone. This fault zone juxtaposes coarse and fine members of the Puente Formation and thrusts bedrock over late Pleistocene alluvium. Although this fault has been active since the late Pleistocene, the recency of activity on this fault zone could not be well constrained.

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4.0 DISCUSSION

4.1 Timing of Holocene Earthquakes on the Chino Fault

The zone of distributed high-angle faults exposed in McMasters Canyon last moved prior to ~3.3-3.5 ka based on radiocarbon dates from the unfaulted debris flow unit (Qd) exposed in trench 1. Strong soil formation on the unfaulted colluvium beneath the debris flow suggests the colluvium is significantly older than the debris flow. Thus, the high-angle faults exposed in McMasters Canyon likely broke prior to the mid-Holocene. Paleoseismic trenches on the north end of the Chino fault constrain the last event on the Chino fault to after ~11.2 ka (Walls and Gath, 2001). Assuming that the last event on the Chino fault ruptured the length of the fault between the trench sites, and that the faults exposed within McMasters Canyon slip during earthquakes on the Chino fault, our investigation constrains the timing of the last event between ~3.3 and ~11 ka, and most likely between about ~5 and ~11 ka. The lack of fresh-looking scarps along the Chino fault suggest that some time has elapsed since the last rupture, which is consistent with our findings.

4.2 Slip Partitioning along a structural complexity on the southern Chino fault

The presence of discrete low-angle and high-angle faults within the Chino fault zone in the McMasters Canyon area suggests that slip may be partitioned between these structures. The high dip and mismatched bedrock stratigraphy across some of the faults exposed in trenches 1 and 2 indicates that these faults accommodate lateral motion. The low angle of the fault zone exposed in trenches 5 and 6, and the faulting of bedrock over older alluvium in trench 5 suggests that this structure accommodates dip-slip motion. The intense deformation observed on the low-angle faults and diffuse minor deformation observed on the high-angle faults suggest that slip is not partitioned equally between these faults. The low-angle fault accommodates most of the movement on the Chino fault in the study area. The stronger development of dip- slip structures may be due to a left step in the Chino fault (Figures 2 and 5). Left

37 NEHRP Report 04HQGR0107 steps on right lateral faults typically result in compressional structures along the fault. This explains why dip-slip faulting in our study area is so much better developed than the lateral slip structures. The left step occurs just north of the study site. North of the stepover, the fault is flanked on the west by the Mahala anticline and on the east by the Slaughter folds, whose orientation suggests a component of right slip. To the south, the Chino fault is at a high-angle to the east-trending fold-fault belt from Arena Blanca-syncline southward. North of the stepover, bedding in HW and FW tend to intersect the fault at right angles, except for near-fault drag. One interpretation is that Chino fault offset began as a vertical strike-slip fault, and later the Chino fault was folded along the Mahala anticline to its present reverse separation. A similar explanation was demonstrated for the San Gabriel fault southeast of Bouquet Canyon based on deformation of the Pleistocene Saugus Formation at Saugus Oil Field.

4.3 Slip budget between the Elsinore fault and the Puente Hills

We address here the problem of the decrease in slip rate between the Elsinore fault and the Whittier fault, a decrease too large to be accommodated by right-lateral strike slip on the Chino fault. At Glen Ivy Marsh, the strike-slip rate on the Elsinore fault is 5.3-5.9 mm/yr (Millman and Rockwell, 1986), with evidence for 4 to 5 earthquakes of M 6-7 since about 1060 A.D. (Rockwell et al., 1986) The last event was probably the M6 Temescal Valley earthquake of May 15, 1910 (Rockwell, 1989). To the northwest, the Whittier fault at Santa Ana Canyon has a slip rate of 2 to 3 mm/yr based on a 200-m horizontal offset of Santa Ana River terraces 140 kyr in age (Rockwell et al., 1988; Gath et al., 1988; Gath, 1997). Farther west, at Olinda Creek, one strand of the Whittier fault has a minimum slip rate of about one mm/yr. A stream offset by this strand is offset the same amount by another strand of the fault, leading Gath et al. (1992) and Rockwell et al. (1992) to assign a slip rate of two mm/yr across both strands, consistent with the offsets at

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Santa Ana Canyon. The problem is to account for the difference of about 3 mm/yr between slip rates on the Elsinore and Whittier faults. A difficulty in estimating young displacement on the Whittier fault is that the fault reactivated a Miocene normal fault (Yeats and Beall, 1991; Bjorklund et al., 2002) that might have been accompanied by an unknown component of Miocene strike slip. Similarly, the Chino fault is parallel to the Prado-Corona normal fault and similar faults to the west that have little or no displacement younger than Sycamore Canyon, suggesting that the Chino fault is a reactivated late Miocene normal fault. A second possibility is that part of the displacement is accompanied by rotation, as is the case in the San Fernando Valley and east Ventura Basin (Levi and Yeats, 2004). The Santa Rosa Basalt, dated at 10.6 Ma, is offset across the Elsinore fault no more than 15 km (Hull and Nicholson, 1992). The westward-increasing gradient in potassium-argon ages of the Peninsular Ranges batholith is offset 11-12 km across the Elsinore fault (Gray et al., 2002). The total right separation on the Whittier fault is 8-9 km based on offset facies and isopachs of Paleogene strata (McCulloh et al., 2000). This estimate faces the difficulty that the Paleogene facies boundaries turn abruptly westward north of the Whittier fault. In addition, Bjorklund and Burke (2002) constructed isopachs of the Sycamore Canyon Member that they interpreted as showing no strike slip across the Whittier fault, although the isopachs south of the fault, where there is well control, are parallel to the fault, and an undetermined amount of strike slip is permitted by their isopach data. In summary, although the total offset across the Elsinore fault appears greater than that across the Whittier fault, the uncertainties in all offset estimates preclude a conclusion that the offsets across the Whittier fault are less than those across the Elsinore fault. The discrepancy between the slip rate at Glen Ivy Marsh and that in Santa Ana Canyon may be accommodated on several structures: (1) The Chino fault could take up about 0.5 mm/yr, dying out at the north end of the Chino Hills. (2) The East Coyote anticline, part of the Puente Hills thrust system, takes up about 1.3

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± 0.5 mm/yr of shortening based on dislocation modeling (Myers et al., 2003), a rate similar to rates for the Puente Hills blind thrust farther west (Shaw et al., 2002). The East Coyote blind fault has accumulated 1.5 km offset over the past 1.5 m.y. (Myers et al., 2003). (3) Folds associated with slip on the Whittier fault (Harding, 1974; Bjorklund and Burke, 2002) uplift the northern edge of the La Habra syncline and contribute to uplift of the Puente Hills north of the Whittier fault. These folds represent a partitioning of strain between blind thrusting and folding and nearly pure strike slip as measured in trenches. The folds have tectonic expression and are assumed to be active. (4) Folds and faults in the southeastern Puente Hills, including the Arena Blanca syncline and the Scully Hill fault, represent distributed shortening that might be accommodated on a single blind thrust at depth. The balance of the slip rate difference between the Elsinore and Whittier faults may be taken up by uplift of the northern end of the Santa Ana Mountains at a rate of 0.3- 0.4 mm/yr, accommodated either by blind thrusting or by a change in the Elsinore fault to a more westerly-striking, lower-dipping thrust (Gath et al., 2002).

5.0 CONCLUSIONS

This study produced the following results on the recency of activity and style of deformation for the Chino fault:

• A diffuse, 30-40 m-wide zone of distributed high-angle faulting coincident with the mapped trace of the Chino fault does not cut a debris flow with a calibrated AMS 14C age of ~3.2-3.5 ka. The development of a strong soil on unfaulted colluvium underlying the debris flow suggests the fault has not ruptured since at least the mid-Holocene. When combined with a maximum age of ~11 ka for the last rupture from a trench site at the north end of the Chino fault, our findings suggest the most recent event occurred in the early to mid-Holocene.

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• Deep excavations within McMasters Canyon reveal that stream channel deposits postdate the last earthquake on the Chino fault. This suggests that the canyon was deeply eroded and refilled following the last earthquake. Thus, using channel deposits to determine slip rate for the Chino fault is not possible at this site.

• A significant low-angle fault zone upslope of the mapped trace of the Chino fault cuts Pleistocene fan/terrace deposits. This fault does not cut overlying young surficial soil horizons.

• A left-bend or step in the Chino fault immediately north of the paleoseismic site may cause localized uplift and partitioning of slip across the project area. The diffuse, high-angle fault zone exposed in the canyon may accommodate lateral slip and the low angle dip-slip fault zone found upslope of the high angle fault zone may accommodate dip slip motion.

• No trace of the Chino fault has been found north of the Chino Hills as based on subsurface data in the Los Serranos area. In addition, the two folds parallel to the Chino fault, the Mahala anticline and Ridge Syncline, also die out at the same latitude at the north end of the Chino Hills. Vertical separation of a prominent bedrock contact, the base of the Sycamore Canyon Member of the Puente Formation decreases to zero at the northern end of the Chino Hills.

• The strike-slip rate on the Elsinore fault is lower on the Whittier fault to the northwest. Some of the slip-rate could be taken up in the Chino fault, but even though there is evidence for right-lateral displacement, it must be small because the Chino fault dies out at the northern end of the Chino Hills. Additional right slip is taken up on the Coyote Hills fold and thrust, which includes the Puente Hills thrust to the west. Finally, there may be a blind

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thrust uplifting the northern end of the Santa Ana Mountains, which are converging northward against a fold-thrust belt in the southern Puente Hills, in the vicinity of the water gap filled by Santa Ana Canyon.

• The seismic hazard posed by the Chino fault would appear to be low based on the slip rates and earthquake timing determined in this study. However, the structural complexities and sedimentation at the site were not optimal for detailed paleoseismic analysis, and as such, this conclusion should be considered in that context.

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APPENDIX 1: REFERENCES

Bjorklund, T., and Burke, K., 2002, Four-dimensional analysis of the inversion of a half-graben to form the Whittier fold-fault system of the Los Angeles Basin: Jour. Structural Geology 24:1369-1387. Bjorklund, T., Burke, K., Zhou, H., and Yeats, R.S., 2002, Miocene rifting in the Los Angeles Basin: Evidence from the Puente Hills half-graben, volcanic rocks, and P-wave tomography: Geology 30:45`-454. California Division of Water Resources, 1970, Meeting water demands in the Chino-Riverside area: Appendix A – Water supply: California Dept. of Water Resources Bull. 104-3, 108 p. Castro, M.J., 1975, Mahala field, in A tour of the oil fields of the Whittier fault zone, Los Angeles basin, Calif.: Pacific Section AAPG-SEG-SEPM Joint Annual Field Trip, Long Beach, California, April 26, 1975, p. 73-76. Critelli, S., Rumelhart, P.E., and Ingersoll, R.V., 1995, Petrofacies and provenance of the Puente Formation (middle to upper Miocene), Los Angeles Basin, southern California: Implications for rapid uplift and accumulation rates: Jour. Sedimentary Research, A65:656-667. Daviess, S.N., and Woodford, A.O., 1949, Geology of the northwestern Puente Hills, Los Angeles County, California: U.S. Geol. Survey Oil and Gas Preliminary Investigations Map 83, scale 1:24,000. Dibblee, T.W., Jr., 2001a, Geologic map of the Whittier and La Habra quadrangles: Dibblee Geological Foundation Map DF-74, scale 1:24,000. Dibblee, T.W., Jr., 2001b, Geologic map of the Yorba Linda and Prado Dam quadrangles, (eastern Puente Hills): Dibblee Foundation Map DF-75, scale 1:24,000 Durham, D.L., and Yerkes, R.F., 1964, Geology and oil resources of the eastern Puente Hills area, southern California: U.S. Geol. Survey Prof. Paper 420-B, 62 p.

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Eldridge, G.H., and Arnold, R., 1907, The Santa Clara Valley, Puente Hills, and Los Angeles oil districts, southern California: U.S. Geol. Survey Bull. 309, 366 p. French, J.J., 1972, Ground water outflow from Chino Basin, upper Santa Ana Valley, southern California: U.S. Geol. Survey Water-Supply Paper 1999-C, 28 p. Gaede, V.F., 1969, Prado-Corona oil field: California Div. Oil and Gas Summary of Operations 55(1):22-29, 4 pl. Gath, E.M., 1997, Tectonic geomorphology of the eastern Los Angeles Basin: U.S. Geol. Survey Final Technical Report, National Earthquake Hazards Reduction Program Award 1434-95-G-2526, 13 p. Gath, E.M., Hanson, J.H., Clark, B.R., and Rockwell, T.K., 1988, The Whittier fault in southern California: Preliminary results of investigations: EOS 69:260. Gath, E.M., Gonzalez, T., and Rockwell, T.K., 1992, Slip rate on the Whittier fault based on 3-D trenching at Brea, southern California: Geol. Soc. America Abstracts with Programs 24:26 Gath, E.M., Runnerstrom, E.E., and Grant, L.B., 2001, Active deformation and earthquake potential of the southern Los Angeles Basin, Orange County, California: U.S. Geol. Survey Final Technical Report, National Earthquake Hazards Reduction Program Award 01HQGR0117, 27 p. Gray, C.H., Jr., 1961, Geology of the Corona South quadrangle and the Santa Ana Narrows area, Riverside, Orange, and San Bernardino counties, California: California Div. Mines Bull. 178. 120 p. Gray, C.H., Jr., Morton, D.H., and Weber, F.H., Jr., 2002, Geologic map of the Corona South 7.5’ quadrangle, Riverside and Orange counties, California: U.S. Geol. Survey Open-File Report 02-21, map scale 1:24,000. Harding, T.P., 1974, Petroleum traps associated with wrench faults: AAPG Bull. 59:1290-1304. Hauksson, E., 1990, Earthquakes, faulting, and stress in the Los Angeles Basin: Jour. Geophys. Research 95:15,365-15.394.

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Hauksson, E., and Jones, L.M., 1991, The 1988 and 1990 Upland earthquakes: Left-lateral faulting adjacent to the central Transverse Ranges: Jour. Geophys. Research 96:8143-8165. Hauksson, E., Hutton, K., Jones, L., and Given, D., 2002, The M4.8 Yorba Linda, Orange County, earthquake of 3 Sept. 2002: Preliminary report, Southern California Seismic Network/TriNet, update 09/13/2002, 2 p. Heath, E.G., Jensen, D.E., and Lukesh, D.W., 1982, Style and age of deformation on the Chino fault, in Neotectonics in Southern California, volume and guidebook, J.D. Cooper, ed., Geol. Soc. America Cordilleran Section, 78th Annual Meeting, Anaheim, California, 43-51. Kleinpell, R.M., 1938, Miocene Stratigraphy of California: Tulsa, OK, AAPG, 450 p. Krueger, M.L., 1943, Chino area, Los Angeles Basin and southernmost California: California Div. Mines Bull. 118:362-363. Lang, H.R., 1978, Late Cretaceous biostratigraphy of the southeastern Los Angeles Basin: California Division of Oil and Gas Report TR20, 15 p. Levi, S., and Yeats, R.S., 2003, Paleomagnetic definition of crustal fragmentation and Quaternary block rotations in the east Ventura Basin and San Fernando Valley, southern California: Tectonics 22(5), 1961:doi:10.1029/2002TC001377, 15 p. Luyendyk, B.P., 1991, A model for Neogene crustal rotations, transtension, and transpression in southern California: Geol. Soc. America Bull. 103:1528-1536. McCulloh, T.H., Beyer, L.A., and Enrico, R.J., 2000, Paleocene strata of the eastern Los Angeles Basin, California: Paleogeography and constraints on Neogene structural evolution: Geol. Soc. America Bull. 112:1155-1178. McCulloh, T.H., Beyer, L.A., and Morin, R.W., 2001, Mountain Meadows Dacite: Oligocene intrusive complex that welds together the Los Angeles Basin, northwestern Peninsular Ranges, and central Transverse Ranges, California: U.S. Geol. Survey Prof. Paper 1649, 34 p.

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McCulloh, T.H., Fleck, R.J., Denison, R.E., Beyer, L.A., and Stanley, R.G., 2002, Age and tectonic significance of volcanic rocks in the northern Los Angeles basin, California: U.S. Geol. Survey Prof. Paper 1669, 24 p. Millman, D.E.,and Rockwell, T.K., 1986, Neotctonics of the Elsinore fault in in Temescal Valley, California, in Neotectonics and Faulting in Southern California, volume and guidebook, Geol. Soc. America Cordilleran Section, 159-165. Morton, D.M., and Gray, C.H., Jr., 2002, Geologic map of the Corona North 7.5’ quadrangle, Riverside and San Bernardino counties, California: U.S. Geol. Survey Open-File Report 02-22, scale 1:24,000. Myers, D.J., Nabelek, J.L., and Yeats, R.S., 2003, Dislocation modeling of blind thrusts in the eastern Los Angeles Basin, California: Jour. Geophys. Research 108(B9), doi: 10.1029/2002JB002150, 18 p. Olson, L.J., 1977, Mahala oil field and vicinity: California Div. Oil and Gas Report TR18, 14 p. Powell, C.L., II, and Stevens, D., 2000, Age and paleoenvironmental significance of mega-invertebrates from the “San Pedro” Formation in the Coyote Hills, Fullerton and Buena Park, Orange County, southern California: U.S. Geol. Survey Open-File Report 00-319, 83 p. Prothero, D.R., and Donohoo, L.L., 2001, Magnetic stratigraphy of the lower Miocene (Hemingfordian) Sespe-Vaqueros formations, Orange County, California, in Prothero, D.R., ed., Magnetic stratigraphy of the Pacific Coast Cenozoic: Fullerton, California, Department of Geological Sciences, California State University at Fullerton, Pacific Section, SEPM Book 91:242-253. Prothero, D.R., and Lopez, R.A., 2001, Magnetic stratigraphy and tectonic rotation of the upper Paleocene Silverado Formation, Orange County, California, in Prothero, D.R., ed., Magnetic stratigraphy of the Pacific Coast Cenozoic: Fullerton, California, Department of Geological Sciences, California State University at Fullerton, Pacific Section, SEPM Book 91, p. 27-36.

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Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Bertrand, C., Blackwell, P.G., Buck, C.E., Burr, G., Cutler, K.B., Damon, P.E., Edwards, R.L., Fairbanks, R.G., Friedrich,M., Guilderson, T.P., Hughen, K.A., Kromer, B., McCormac, F.G., Manning, S., Bronk Ramsey, C., Reimer, R.W., Remmele, S., Southon, J.R., Stuiver, M., Talamo, S., Taylor, F.W., van der Plicht, J., and Weyhenmeyer C.E., 2004, Radiocarbon 46:1029-1058. Rockwell, T.K., 1989, Behavior of individual fault segments along the Elsinore- Laguna Salada fault zone, southern California and northern Baja California: Implications for the characteristic earthquake model, in Schwartz, D.P., and Sibson, R.H., eds., Fault Segmentation and Controls of Rupture Initiation and Termination: U.S. Geol. Survey Open-File Report OF 89-315, 288-308. Rockwell, T.K., McElwain, R.S., Millman, D.E., and Lamar, D.L., 1986, Recurrent late Holocene faulting on the Glen Ivy North strand of the Elsinore fault at Glen Ivy Marsh, in Neotectonics and Faulting in Southern California, volume and guidebook, Cordilleran Section, Geol. Soc. America, 167-175. Rockwell, T.K., Gath, E.M., and Cook, K.D., 1988, Sense and rate of slip on the Whittier fault zone near Yorba Linda, California: Geol. Soc. America Abstracts with Programs 20:224. Rockwell, T.K., Gath, E.M., and Gonzalez, T., 1992, Sense and rate of slip on the Whittier fault zone, eastern Los Angeles Basin, California: Proc. 35th Annual Meeting, Assoc. Engineering Geologists, 2-9 October; in Stout, M.L., ed., Assoc. Engineering Geologists, Santa Ana, California, 679. Schoellhamer, J.E., Kinney, D.M., Yerkes, R.F., and Vedder, J.G., 1954, Geologic map of the northern Santa Ana Mountains, Orange and Riverside counties, California: U.S. Geol. Survey Oil and Gas Investigations Map OM-154, scale 1:24,000 Schoellhamer, J.E., Vedder, J.G., Yerkes, R.F., and Kinney, D.M., 1981. Geology of the northern Santa Ana Mountains: U.S. Geol. Survey Prof. Paper 120-D, 109 p., map. 1:24,000.

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Shaw, J.H., Plesch, A., Dolan, J., Pratt, T.L., and Fiore, P., 2002, Puente Hills blind thrust system, Los Angeles, California: Seismol. Soc. America Bull. 92:2948- 2960. Smith, D.P., 1977, Chino fault: California Division of Mines and Geology Fault Evaluation Report 38, 11 p., map scale 1:24,000. Tan, S.S., Miller, R.V., and Evans, J.R., 1984, Environmental geology of parts of the La Habra, Yorba Linda, and Prado Dam quadrangles, Orange County, California: California Div. Mines and Geology Open-File Report 84-24LA, 119 p. Teissere, R.F., and Beck, M.E., 1973, Divergent Cretaceous paleomagnetic pole positions for the Southern California batholith, USA: Earth and Planet. Sci. Lett. 18:297-300. Treiman, J.A., 1991, Whittier fault zone, Los Angeles and Orange counties: California Div. Mines and Geology Fault Evaluation Report FER 222, 17 p. Treiman, J.A., 2002a, Chino fault, Riverside and San Bernardino counties, California: California Geol. Survey Fault Evaluation Report FER 247, 18 p., 3 pl. Treiman, J.A., 2002b, Tin Mine, Main Street, Eagle and Glen Ivy (North and South) fault strands of the Elsinore fault zone, Riverside County, California: California Geol. Survey Fault Evaluation Report FER 248, 13 p. 4 figs., 3 pl. Walls, C., and Gath, E.M., 2001, Tectonic geomorphology and Holocene surface rupture on the Chino fault: Southern California Earthquake Center Annual Meeting, Proceedings and Abstracts, p. 118, reprinted in Treiman, 2002a. Weber, F.H., Jr. 1977, Seismic hazards related to geologic factors, Elsinore and Chino fault zones, northwestern Riverside County, California: California Division of Mines and Geology Open-File Report 77-4, 96 p., 4 pl., map scale 1:24,000 Wissler, S.G., 1943, Stratigraphic relations of the producing zones of the Los Angeles oil fields: California Division of Mines Bull. 118, p. 209-234.

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Wissler, S.G., 1958, Correlation chart of producing zones of Los Angeles Basin oil fields, in Higgins, J.W., ed., A guide to the geology and oil fields of the Los Angeles and Ventura regions: Los Angeles, Pacific Section, AAPG, p. 59-61. Woodford, A.O., Shelton, J.S., and Moran, T.G., 1944, Stratigraphy and oil possibilities of the Puente and San Jose Hills, California: U.S. Geol. Survey Preliminary Investigation Map 23, scale 1:75,000. Woodford, A.O., Moran, T.G., and Shelton, J.S., 1946, Miocene conglomerates of Puente and San Jose Hills: AAPG Bull. 30:514-560. Woodford, A.O., Shelton, J.S., Doehring, D.O., and Morton, R.K., 1971, Pliocene- Pleistocene history of the Perris Block, southern California: Geol. Soc. America Bull. 82:3421-3449. Wright, T.L., 1991, Structural geology and tectonic evolution of the Los Angeles Basin, in Biddle, K.T., ed., Active Margin Basins: AAPG Memoir 52:35-134. Yeats, R.S., 2004, Tectonics of the San Gabriel Basin and surroundings, southern California: Geol. Soc. America Bull. 116:1158-1182. Yeats, R.S., and Beall, J.M., 1991, Stratigraphic controls of oil fields in the Los Angeles Basin: A guide to migration history: in Biddle, K.T., ed., Active Margin Basins: AAPG Memoir 52:221-235. Yerkes, R.F., 1972, Geology and oil resources of the western Puente Hills area, southern California: U.S. Geol. Survey Prof. Paper 420-C, 63 p.

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APPENDIX 2: WELLS USED IN CROSS SECTIONS IN FIGURE 3

Cross Section A-A’. 1. Norman Fuller; 2. Patton Three Corners and Shell Puente Core Hole 4 (projected); 3. Lee Core Hole 2; 4. Lee Core Hole 4; 5. Southern Counties Petroleum and Drilling. Cross Section B-B’. 6. Hillman Long Pellissier; 7. Westates Kraemer; 8. Lovelady Supply Robertson Kraemer; 9. Scott Chino 2. Cross Section C-C’. 10. James Michelin Borba; 11. Union Newman; 12. Fowler % Stansbury Borba 1A; 13. C&C Van Hofwegen; 14. Scott Chino 1. Cross Section D-D’. 15. Casex Fleet Signal Bryant; 16. Casex East Puente Fee 4 o.h.; 17. Casex Abacherli 6; 18. Texaco (Getty) Abacherli; 19. Hancock Abacherli 1A; 20. Michelin Abacherli; 21. Fairfield Elena. Cross Section E-E’. 22. Casex Mollin 2; 23. Casex Lamb rd. 1; 18. Texaco Abacherli; 24. KMT Abacherli 4; 25. Casex Gov. 159-1; 26. Casex Gov. 156-1; 27. Cherrydale; 28. Airways Santa Anaheim. Cross Section F-F’. 29. L&M Hudson 1; 30, L&M Hudson 2; 31. Atlantic Aros; 32. Pradp Gov. TMPC-1; 33. Alpoil Gov. C-1; 34. Alpoil Gov. TMPD-1; 35. Prado Gov. 176-1; 26. Prado Sardco 4 Cross Section G-G’. 37. Cree Prado Gov.; 38. A.L. Hunter Sardco 2 o.h.; 39. Prado Sardco 10; 40. Prado Sardco 5; 41. Prado Sardco 3; 42. Prado Sardco 1; 43. Santa Fe Minerals Sardco 1. Cross Section H-H’/ 44. Draucker Shaw; 45. Draucker Draucker; 46. Hampton SFLI Quinn 3; 47. Hampton SFLI Quinn 2; 48. Hampton SFLI Quinn 1 rd. 1

Abbreviations: o.h., original hole; rd. 1, first redrilled hole. If no well number is given, number 1 is assumed. Wells located on Figure 2 and on California Division of Oil, Gas, and Geothermal Resources Maps 109 and W-6. Well files curated at repository at California State University at Long Beach.

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APPENDIX 3: PLATES

Plate 1. Logs of the south walls trenches 1 through 4 Plate 2. Logs of both walls of trench 5 and the south wall of trench 6

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800 760 680 820 780 740 720 700 N 58 METERS 56 840 660 NORTHWEST CANYON WALL

860 54 52 Trench 1

640 50 620 48 S85W 600 46 Trench2 44 Trench 4 42 Trench 3 5m to end 40 of trench 38

EXPLANATION 36 Massive Fault; measured strike shown in trenches TRENCH 1 A Qyc Trench 6 Trench 5 34 Zone of closely spaced faults SOUTH WALL Holocene Alluvium Pleistocene Alluvium A/B Tsc 0 20 40 60 80 100 32 0.9m step

920 in trench wall 900 860 S61W 880 Meters 30 Massive 940 Contour interval: 5 feet; 1.52 m 28 Massive 26 F: N45W, 82E 0.8m step Fracture: N33W, 55NE F: N15W, 90 22 24 in trench wall F: N28W, 80NE 20 18 F: N28W, 80SW 16 14 10 12 Tsc Bedded 8

Soil peds become A Massive bedrock; highly fractured, fissile thinner and longer, 1m step in trench wall TRENCH 2 24 METERS 24 Slough Discontinuous beds: SOUTH WALL Bt1 N30W, 30SW 22 20 A Soil peds dip Fault or fracture with gouge 18 Slough to the southeast 16 BC Massive Qya2 Zone of closely spaced 14-C-T1-4 high angle fractures; Fracture: 14-C-T1-3 ~N69W, 61SW

slough 0.40 meter step N16?E, 80SE CaCO3 lining S61W root pores with Qd some ped faces Massive 1 meter step Clay-lined fractures 14-C-T1-1 ? 3170+/-40 BP ? Weathered slough bedrock Bt2Bt2 ? ? ? ? Red clay layer BC Massive bedrock; highly fractured, fissile; Qya3 fracture orientations highly variable T2-3 Qc

T2-2 Porous Bedrock elevation on Siltstone and granitic clasts Qc opposite wall in clayey silt matrix Trench Bedding: N30W, 20SW continues 4m Carbonate zone

Fault: N25W, 90 Tsc Bedrock fault separation unknown on opposite wall: N20W, ~90 does not cut Fracture overlying colluvium Bedrock fault on opposite wall: N60W, 62NE; does not cut overlying colluvium; not apparent on south wall

EXPLANATION 16 METERS SOUTHEAST CANYON WALL UNIT DEPOSITS DESCRIPTION AGE 14 TRENCH 4 12 METERS Qya1 Young Channel Alluvium Silty Sand with abundant coarse Gravel and Cobbles. Very loose and friable. Modern SOUTH WALL 10 Qya2 Young Channel Alluvium Silty Sand with scattered Gravel and Cobbles. Friable. Latest Holocene 12 TRENCH 3 8 Qya3 Young Channel Alluvium Silty Sand with scattered Gravel and Cobbles. Late Holocene SOUTH WALL Qyc Young Colluvium Modern/Latest Holocene 10 6 Active hillslope colluvium. Clayey Sand and Silt with scattered fine Gravel. Qd Debris Flow Fine Gravel in a Clayey matrix. Mid to late Holocene 4 (3,170+/-40) 2 bench Qc 1/2 Colluvium Clayey fine Sand and Silt, locally with fine Gravel. Early to mid Holocene (?) S30W 0 Qal Alluvium Fluvial Sand and Gravel: Terrace deposit. Late Pleistocene (?) Qc1 Tsc Puente Formation Bedded to Massive fine Siltstone and Sandstone. Rare Conglomerate. Miocene Siltstone Facies of Soquel Member S50W BEDROCK DEPOSITS SOILS CONTACTS Dashed where gradational Bedded siltstone A Tsc Charcoal A Horizon Depositional Fault ? T2-2 Clay Sand sample Massive siltstone Bt Argillic Horizon Soil ? with columnar peds Fault? Qc2 Silt Gravel Bench Fracture ? C ? Sandstone C Horizon bench

3-D Paleoseismic Trenching of the Southern Chino Fault Tsc PLATE 1 CANYON TRENCHES 800 760 680 820 780 740 720 700 N

840 660

860

Trench 1

640 620

600 Trench2

Trench 3 Trench 4 TRENCH 5 18 METERS SOUTH WALL TRENCH 5 EXPLANATION 16 NORTH WALL (flipped) Fault; measured strike shown in trenches Trench 6 Trench 5 Zone of closely spaced faults 14 Holocene Alluvium Pleistocene Alluvium

0 20 40 60 80 100

920 900 12 880 860 Meters A 940 Contour interval: 5 feet; 1.52 m A 10 A2 A Tsc A2 8 Bt 6 Tsc Qoa Qoa Bedding 4 ? Fault: 0 2 Bt N32°W, 25-45°SW Horizontal fault

? Horizontal A fault Qoa Carbonate-lined TRENCH 5 fractures NORTH WALL (flipped)

S50W

Bt A

Qoa Fault: N30°W, 5-48°SW

Fault: Horizontal N32°W, 42-53°SW fault Carbonate-lined fractures AC IEA LINE MATCH TRENCH 6 SOUTH WALL

12 Abundant irregular fractures; abundant carbonate along fractures and bedding; 10 minor remnant bedding and locally crushed 8

Fracture: 6 N70°W, 31°SW Bedding: 4 N7°W, 47°W Fracture: Fracture: 2 N53°E, 78°NW N38°E, 72°SE Bedding: N33°W, 52°SW 0 Fracture: Bedding: N65°W, 39°SW N15°E, 37°NW Fracture: Fracture: N50°W, 75°SW METERS Tsc Fracture: N42°W, 73°SE Fracture: A Fracture: N57°E, 82°SE N47°W, 74°SW N4°W, 74°SW Fracture: Bedding: N25°W, 32°NE Bt Siltstone crushed N10°W, 34°SW 46 Qc and brecciated; carbonates diffused 44 Bedding: throughout N10°W, 28°SW

Bench 1 42 Thinly interbedded grey siltstone and silty very fine sandstone 40 Bedding: BQc N25°W, 32°SW 38

Very weathered siltstone Little remnant bedrock structure 36 A 34 32 30 A

Tsc Sandstone blocks Conglomerate blocks inn a carbonate matrix

A

Mix of soil and bedrock Fault: 26 N8°W, 55°SW;

25 Crushed conglomerate Faults: infused with carbonate N28°W, 57; °SW; Fault; N5°E, 72°SW juxtaposes conglomerate Tsc 24 SHEAR ZONE against silty clay;

MATCH LINE A abundant carbonate-lined Shears: pebbles along shear zone shears in a silty clay matrix; N7°W, 15°SW Fracture: no original bedrock fabric N25°W, 32°SW Bedding: N40°W, 57°SW Fracture: N47°W, 49°SW

EXPLANATION . 3-D Paleoseismic Trenching UNIT DESCRIPTION AGE of the Southern Chino Fault Qc Colluvium Silty fine Sandy Clay with scattered Pebbles and small Cobbles. Early to mid Holocene (?) Qoa Older Alluvium Clay Silt with lenses of Sand and Gravel. Late Pleistocene PLATE 2 Tsc Puente Formation Bedded to Massive fine Siltstone; locally with Sandstone interbeds. Miocene Siltstone Facies of Soquel Member Tsc Puente Formation Massive Sandstone and Conglomerate, locally weakly bedded. Miocene Conglomerate Facies of Soquel Member HILLSLOPE TRENCH

BEDROCK DEPOSITS SOILS CONTACTS Dashed where gradational A1 A Horizon A2 Depositional Fault k Bedded siltstone Sandstone Clay Sand Bt Argillic Horizon Soil Krotavina Massive siltstone Conglomerate Silt Gravel Bench Fracture C C Horizon