Annual Field Trip Number 36, Stops and Discussions June 19 and 20, 2010 Geology and Hydrology in the Eastern San

Gabriel Mountains A Journey through the River of Time

Saturday, June 19, 2010 (Kenney, Reynolds, Goetz, Harris, and El-Zaynab field presentations) #A1: Lost Lake: A Sag Pond and Terraces along the San Andreas Fault #A2: Cosy Dell Formation (K-T Boundary) #A3: Vaqueros-Cosy Dell Fm. Contacts #A4: Crowder Formation Outcrops #A5: Cajon Valley Formation, Victor Valley Fan & Cajon Fault #A6: Vincent Gap and Grassy Hollow (Lunch Stop) #A7: Slope Stability Project at the Angeles Hwy 2 Bridge

Sunday, June 20, 2010 (Nourse, Saint , and Summers field presentations) #B1: Cow Canyon Saddle Overlook #B2: USFS Visitor’s Center #B3: Gneiss-Dikes Intrusions and 1938 Floods #B4: Manker Flats and San Antonio Falls (Lunch Stop) #B5: 1969 Flood Terraces and SAF Outcrop #B6: San Antonio Dam Overlook

Introduction to Geology and Hydrology in the Eastern San Gabriel Mountains

The eastern San Gabriel Mountains, as illustrated by the oblique aerial view on the cover page and the geological cross-section (Figure 1) constitute a spectacular field laboratory for geological and hydrological processes and their interaction with ecology and human activities. The San Gabriel Mountain block is bounded by the Frontal thrust faults (Sierra Madre-Cucamonga Systems), in the south and the San Andreas Fault System, a right-lateral transform fault system, that now forms the plate boundary between the Pacific and the North American plates, The mountains are dissected by right- lateral and left-lateral strike slip faults, many of which are accentuated by deep canyons, forming the headwaters of our river systems. During this trip we will encounter the San Gabriel River, the San Antonio Creek, the Lytle Creek and the Cajon Creek and examine their response to tectonic shifts, floods, landslides and fires.

On the first day we will visit the San Andreas Fault System in the Cajon Pass and in the Wrightwood area, under the leadership of Miles Kenney, Bob Reynolds, Chris Goetz and Chris Harris. On the second day we will visit the San Antonio Creek, from its source to the mouth, examining its response to the San Antonio left-lateral strike slip fault, the landslides, the floods, the fires and the dam, under the leadership of Jon Nourse of CalPoly Pomona, who has done field work and supervised student theses since 1991. We will be camping at the Mt. Baldy Ranch Road R.V. Park in the Cow Canyon Saddle, overlooking the San Gabriel Fault and at the tow of the Cow Canyon Landslide.

Figure 1. Geological cross-section across the eastern San Gabriel Mountains, with several of the formations and the faults that we will encounter during the field trip. (from NAGT Field Guide, 2001)

ROAD LOG

(compiled by Prem Saint, Boris Zaprianoff and Vik Mathur)

Figure2. East San Gabriel Mountains with stops for Day 1 and Day2

Day 1, Saturday, June 19, 2010

Highlights: San Andreas Fault Zone in the Cajon Pass, Sedimentation Story of the K-T Boundary, Crowder Formation, Cajon Valley Formation; Cajon Fault, Victor Valley Fan, and Slope Stability Project on the Angeles Highway 2 Bridge

0.0 (0.0) Start at Cow Canyon Saddle at the entrance of Mt. Baldy Ranch R.V. Park, 30601 East Glendora Ridge Road, Mt. Baldy, CA 91759, driving down towards Mt. Baldy Village.

0.8 (0.8) Turn right onto Mt. Baldy Road, passing through the village and the school, with outcrops of Pre Cambrian gneisses and landslide deposits and chaparral vegetation.

5.4 (4.6) Turn left on Shinn Road. Cross the bridge on the San Antonio Creek and San Antonio Fire Station, approaching San Antonio Dam on your right. 7.6 (2.2) Curve right onto Mountain Road and San Antonio Heights Village.

9.6 (2.0) Turn left onto the I-210, Foothill Freeway, East ramp, towards San Bernardino.

18.7 (9.1) Exit on I-15 North towards Barstow.

27.4 (8.7) I-215 joins I-15.

31.0 (2.6) At the top of the rise on I-15, we are crossing the trace of the San Andreas Fault, the site of potential disruption following a major earthquake on the fault. To our right (east), two branches of the fault are very close together. To the left (northwest), the fault zone appears as the large, 0.25 mile-wide shear zone of Lone Pine Canyon with fault-related features like Lost Lake, a sag pond.

Figure 3. San Andreas Fault in the Cajon Pass, along with Los Angeles Basin utility lines, railroads, gas pipes, electrical lines which could be severed during future earthquakes, causing severe economic disruptions.

32.8 (1.8) Prepare to exit at Cleghorn Road, 0.5 mile ahead.

33.3 (0.5) Exit at Cleghorn Road.

33.5 (0.2) Stop, TURN LEFT and proceed under the freeway to the junction of Cleghorn Road and Cajon Boulevard. Proceed south toward Blue Cut.

35.3 (1.8) TURN RIGHT onto Swarthout Canyon Road and cross Cajon Creek.

35.8 (0.5) Caution; cross BNSF railroad tracks.

36.3 (0.5) Caution; cross BNSF railroad tracks. Proceed north toward Lost Lak 36.6 (0.3) TURN RIGHT into the parking lot at Lost Lake. Stop A1

STOP A1: LOST LAKE: A SAG POND ALONG THE SAN ANDREAS FAULT, TERRACE DEPOSITS Field Presentations by Miles Kenney and Robert Reynolds

The sag pond at the Lost Lake is a product of groundwater seepage in an area of tectonic depression in the San Andreas Rift Zone, a linear valley in the Lone Pine Canyon. Dr. Ray Weldon conducted a detailed study of a series of stream terraces associated with Cajon Creek in the region of Lost Lake (Weldon and Seih, 1985). The work identified progressive offset of radiocarbon dated, late Pleistocene and Holocene deposits and landforms by the San Andreas fault that yielded a set of slip rates spanning the past 14,400 years. Near Lost Lake they determined a slip rate for the San Andreas fault of ~24 mm/yr for the past 14,400 years and inferred that this slip rate had remained relatively constant during that period of time. The primary data utilized was the identification of a series of stream terraces associated with Cajon Creek that had been progressively offset by the San Andreas fault.

Their findings provided strong constraints on the local kinematics of the San Andreas Fault System in the area. For example, other work by Weldon and others determined a slip rate on the San Andreas fault approximately 10 miles northwest near Wrightwood of ~34 mm/yr which is north of the juncture between the San Jacinto and San Andreas faults. They postulated that the total slip of 34 mm/year near Wrightwood was portioned between the San Jacinto and San Andreas faults in the area of Cajon Valley. The estimated slip rate for the local San Jacinto fault zone is 10 mm/yr, which once added to the estimated 24 mm/yr totaled 34 mm/yr. Figure 4. Lost Lake Sag Pond: Groundwater seepage in the tectonic depression in the San Andreas fault zone has created the pond, here covered with cattails along the shore.

36.9 (0.3) View south of Blue Cut, its color from glaucophane and actinolite schist. From Blue Cut, it is a quick walk from the Pacific Plate across the San Andreas Fault to the North American Plate, to our next stop at the Cretaceous Cosy Dell Formation.

37.9 (1.0) STOP at Cajon Boulevard. Watch for cross-traffic. Proceed diagonally southeast across Cajon Boulevard to the unused north-bound lane of Rte 66.

38.0 (0.1) Stop A2.

STOP A2: COSY DELL FORMATION (K-T BOUNDARY?) Field Presentation by Bob Reynolds

Cajon pass contains 70 million years of history in the rock record. Sediments of Cretaceous age are present as is the Earliest Miocene Vaqueros Fm. Continental deposition starts with the Middle Miocene Cajon Valley Beds. The Inface Bluffs on the northern horizon contain the Brunhes-Matuyama reversal (765,000 yr) suggesting a record of deposition thru the middle-late Pleistocene.

At this stop, between I-15 and old Route 66, we are examining the Cretaceous Cosy Dell Formation (Morton and Miller, 2003), formerly called the Paleocene–Eocene? San Franscisquito Formation (Dibblee, 1967; Woodburne and Golz, 1972). The basal conglomerate is overlain by limey sandstones and dark, silty limestone. Its Cretaceous age is determined by the presence of elasmosaur vertebrae in the outcrop to the west (Kooser, 1985). Articulated vertebrae in an outcrop to the northwest (Whale Mountain) suggest that this large marine reptile died in place and was not reworked from other sediments (Lucas and Reynolds, 1991). The section may have potential to contain the K/T boundary, but none of the abundant fossil fish scales, crustaceans, gastropods, pelecypods, or plants from this outcrop provide additional age control relating to that transition. Paleocene Coccoplithus pelagicus, a nanofossil, Apectodinum plexus, a dinoflagellate, and Turritella pachecoensis, a gastropod, were reported (Fred Berry p. c. to Kooser, 1985; Weaver 1951-56) from apparently similar sediments somewhere in Cajon Pass, but by the 1970s the specimens and locality data could not be found. Return to vehicles.

38.1(0.1) STOP at Cajon Boulevard. Watch for cross traffic. DRIVE NORTH (right) toward the Cleghorn onramp.

39.3 (1.2) Pull right onto the unused northbound lane of Route 66. Stop A3

STOP A3: VAQUEROS –COSY DELL CONTACTS Field Presentation by Bob Reynolds To the northwest is Whale Mountain, where the Vaqueros (?) Formation crops out and is in fault contact with the Cretaceous Cosy Dell Formation. The Vaqueros (?) Formation unconformably overlies crystalline basement rocks and is unconformably overlain by the middle Miocene (Hemingfordian to Barstovian North American land mammal age) Cajon Valley Beds (Woodburne and Golz, 1972; Woodburne, 1991). The Vaqueros Formation contains fossils of an echinoid (Scutella fairbanksi), elasmobranchs, and the mollusks Ostrea titan subtitan, Pecten sespeensis, Crassatella granti and Turritella inezana, the latter two species important in establishing the late, early Miocene age (Woodring, 1942; Woodburne and Golz, 1972).

An unusual dolphin has been described from these Vaqueros (?) marine facies. The fossil is a member of the archaic superfamily Platanistoidea. The superfamily was widely distributed to all ocean basins in the Tertiary, but today is represented only by the endangered fresh-water Ganges River dolphin (Barnes and Reynolds, 2007). The long-snouted skull was a meter in length, and the body was four meters long.

The Cajon Valley Beds (Woodburne 1991; formerly Punchbowl Formation of Woodburne and Golz 1972; Cajon Formation of Meisling and Weldon, 1982, 1989) are exposed to the west. From the south, visible units are Tcv4 (pink), Tcv5 (green), Tcv3 (red and white), and Tcv 2 (white hogbacks). The Cajon Valley beds range in age from approximately 18–14 Ma (Reynolds, 1991). The beds contain fossil horse, camel, deerlets, rodents, and insectivores. Recent BNSF railroad track additions were monitored by paleontologists who recovered bear, rhino, chalicothere, and the first talpid (mole) from the Cajon Valley Beds. The early to middle Miocene age of the beds has been established by land mammal age chronology. Squaw Peak is to the northeast. The Cajon Valley Beds are separated from the Crowder Formation to the east (not visible) by the Squaw Peak fault.

Pliocene and Pleistocene sediments of the Phelan Peak Formation, Shoemaker Gravels, and Noble’s Old Alluvium are present in the in-face bluffs to the north-northwest. Return to vehicles. Proceed north toward Cleghorn onramp.

39.9 (0.6) Pass the junction of Cajon Boulevard and Cleghorn Road. Bear right (east) under the overpass.

40.0 (0.1) Enter I-15 northbound at Cleghorn Road. Stay in the right lane and prepare to exit right onto Highway 138.

41.0(1.0) EXIT at Highway 138 and move to the right lane.

41.3 (0.3) STOP at Highway 138. TURN RIGHT (east) toward Silverwood Lake; pass through Crowder Formation Units 1 and 2.

41.5(0.2) The thin brown paleosols in Crowder Unit 1 have produced significant numbers of fossil taxa (Reynolds, 1991; Reynolds and others, 2008).

41.8 (0.8) TURNOUT (right) and PARK. Stop A4.

STOP A4: CROWDER FORMATION OUTCROPS Field Presentation by Bob Reynolds

The Crowder Formation was named by Dibblee (1967) and described as Pliocene in age. Foster (1980) divided the Crowder Formation into five units and provided detailed information on source areas and paleo-current direction from the northeast. Subsequent workers (Weldon et al., 1984; Weldon, 1985; Meisling and Weldon, 1989) defined the age of the lowest Crowder units based on a local magnetic polarity zonation tied to small mammal assemblages from the paleosols (Reynolds, 1984, 1985, 1991). The first half of the Crowder Formation was estimated to span a period of time that began prior to 17 Ma and ended at than 7.1 Ma (Reynolds and others, 2008). Consequently, the age of the latter part of the Crowder Formation would shed light on structural and erosional events in latest Miocene time, prior to the deposition of the Phelan Peak Formation.

Figure 5. Cajon Pass Geology and Hydrology The view north is in the direction of the Crowder Fm. upper Unit 3 (7.3 Ma). The northern skyline exposes, from the north bound lane of I-15, the Phelan Peak Formation (4.2-1-5 Ma), the Shoemaker Gravels (1.3-0.9 Ma), and Noble’s Old Alluvium (0.8-0.5, contains the Brunhes-Matuyama reversal

This depositional sequence suggests that there may have been a very short time to develop the major unconformity between Crowder Unit 5 (6 Ma) and the Phelan Peak Formation (4.2[765,000 yr]). Ma).

Figure 6. Outcrop of the Crowder Formation, Miocene sediments, with rich mammal, reptile, bird and mollusk fossils, across the road from Stop A4.

Figure 7. Geologic Map showing the Crowder Formation in the Cajon Pass, from USGS, Morton and Miller, 2003

The Crowder Formation is now considered to be a lithologically distinct formation in fault contact with the Cajon Valley beds (Morton and Miller, 2003) with a portion of that deposition contemporaneous, between 18 and 14 Ma (Weldon, 1985; Woodburne, 1991; Reynolds, 1991). The Crowder Formation is nearly 1000 meters thick and is located northeast of the Squaw Peak Fault, while the 3,000 meter thick Cajon Valley beds are located southwest of the fault. The latter contain land mammal fossils representing a period of time between 18 and 14 Ma (Woodburne, 1991; Reynolds, 1991). The Crowder units have produced forty mammalian species, including two new species (Lindsay and Reynolds, 2008). There are reptiles, birds and mollusks from the deposits, as well as the remains of burrowing insects and millipedes. The recovery of more than 12,639 diagnostic fossils from 20 paleosol horizons within the Crowder Formation illustrates the importance of careful examination and collection from buried soil horizons.

View east toward vegetation at Sulfur Spring. To the south, bare cliffs of Crowder Unit 3 result from slope failure. Retrace west to I-15.

42.4 (0.6) STOP at the junction of Hwy 138 and I-15. Park into the McDonald Area Parking Lot for discussion on the Cajon Valley Beds, Victorville Fan and the Cajon Fault.

STOP A5: CAJON VALLEY FORMATION, VICTOR VALLEY FAN & CAJON FAULT Field presentation by Miles Kenney

The Cajon Valley Fault Story:

Total dextral (right lateral) motion between the North American and Pacific Plates during the late Tertiary has primarily been accommodated by a broad zone of offshore and continental shearing on strike slip faults, Basin and Range extension, and transrotation of crustal blocks. Total right lateral motion between the North American and Pacific plates may be as high as 1,100 to 1,500 km during the past 30 Ma. The San Andreas fault (senso stricto in central California, and including the San Gabriel fault system and San Francisquito-Fenner-Clemens Well fault system in southern California) has likely contributed between 300 to 340 km of this total slip. For example, although the 300 km of dextral motion on the SAF north of the Transverse Ranges took place essentially across a relatively narrow zone since the early Miocene and possibly Late Eocene, numerous strands and fault systems have accommodated the motion within and south of the Transverse Ranges in southern California during the same period of time. Therefore, reconstruction of the Late Cenozoic San Andreas Fault System in southern California has involved estimating the timing and magnitude of slip across active strands and inactive strands which were subsequently abandoned and often truncated by younger faults.

The Cajon Valley Fault which is exposed for 13 kilometers along the western margin of Cajon Valley and can be extrapolated more than 20 km parallel to the SAF toward the northwest beneath Victorville Fan deposits. Six piercing planes (lithologic contacts) within the Holcomb Ridge – Table Mountain igneous and metamorphic suite are correlated to exposures of the same suite of rocks in the Western San Bernardino Mountains of the eastern Cajon Valley region. The Cajon Valley fault is the likely candidate for the exhibited displacement between these two terrains. Based on geologic mapping, references to published papers, and thin section analysis, the Cajon Valley fault experienced approximately 27±5 km of right lateral displacement between 4.1 to 9.5 Ma or possibly to 13.5 Ma.

The magnitude of total displacement across the Cajon Valley Fault of ~27 km places kinematic constraints on nearby faults within the San Andreas Fault System. The Cajon Valley Fault was likely the northern strand of the northwestern extension of the SGF, which accumulated 45±15 kilometers of right-lateral motion between 4.5 to 5 and 12 Ma. Thus, the alignment of the Cajon Valley fault as the northern extension of the San Gabriel fault as proposed by others is adopted within the present kinematic model. Since the Cajon Valley Fault probably did not accommodate all the offset attributed to the San Gabriel fault zone, a second fault strand is required to have accrued the missing ~18 km of dextral slip. The most obvious candidate would be a fault zone bounding the

southern edge of the Holcomb Ridge – Table Mountain slice in essentially the same location as the modern San Andreas Fault. This paleo-reconstruction of the Cajon Valley – San Gabriel fault system requires that the modern San Andreas fault likely existed to southern Cajon Valley since ~10 Ma. In addition, it indicates the San Bernardino strand of the modern San Andreas fault did not develop until after the Holcomb Ridge – Table Mountain slice had been removed from the western San Bernardino Mountains. Thus, the modern San Andreas fault to the region of southern Cajon Valley has likely existed since ~10 Ma; however, toward the southeast from Cajon Valley, the modern strand of the San Andreas fault (San Bernardino strand) likely formed around 4 Ma. Other kinematic ramifications of this model indicate that the Squaw Peak Thrusts did not accrue tens of kilometers of displacement as previously proposed by Matti and Weldon (1989). Additionally, the reconstruction geometry of the model indicates that a restraining and releasing bend existed that could account for the progressive compression and extension deformation documented within the Ridge Basin–Liebre Mountain region as proposed by Crowell (1982).

The Victorville Fan Story and the evolution of Western San Bernardino and NE San Gabriel Mountains

An interpretation for the timing and magnitude of late Quaternary uplift within the western San Bernardino Mountains and northeastern San Gabriel Mountains north of the San Andreas Fault is presented based relative age of structures and stratigraphic relationships primarily identified within Pliocene to Pleistocene sediments. These formations include coarse grained proximal fan deposits associated with the Victorville Fan, and finer grained sediments that pre-date deposition of the Victorville Fan. As originally proposed by Meisling and Weldon (1989), the Victorville fan consisting of the Harold Formation, Shoemaker Gravels and Nobles Older Alluvium were deposited time transgressively as sediments were shed off of the San Gabriel Mountains as they moved toward the northwest due to motion across the San Andreas fault. A series of paleo-reconstructions are provided in the presented paper that exhibit the source regions in the San Gabriel Mountains and relative depositional areas in the Victorville fan deposits and tectonic deformation that was occurring during various times of the late Pleistocene.

Figure 9 Structure contour map of pre-Pliocene erosion surfaces in the western Mojave Desert, San Bernardino Mountains, and Table Mountain located in the northeastern San Gabriel Mountains. The contours in the San Gabriel Mountains south of the San Andreas Fault merely follow the existing topography due to lack of age control and documentation of the preserved erosional surfaces in the range. Except for the San Gabriel Mountains, no regions south of the San Andreas and Pinto Mountain faults were contoured. Thin red lines represent Quaternary faults and folds; black regions indicate late Miocene basalt flows

A structure contour map of the regional pre-Pliocene erosion surface in the San Bernardino Mountains and western Mojave Desert provides a key basis for estimating total vertical deformation. (See Kenney Article, this volume). These data indicate that a locus of compression, followed by vertical uplift of 1.0 to 1.6 km in a 4 to 15 km wide zone north of the San Andreas fault, migrated from the western San Bernardino Mountains to the northeastern San Gabriel Mountains during approximately the past 1.5 to possibly 2.0 Ma (Meisling and Weldon, 1989). The uplift produced a north-dipping monocline with fold axis parallel to and on the northern side of the San Andreas fault. The upper limb of the monocline is approximately horizontal between the upper hinge and the San Andreas fault, and narrows in steps toward the northwest. The uplifted monoclinal region is 12 to 14 km wide near eastern Summit Valley, 6 to 10 km near Cajon Valley, 5 to 7 km at Table Mountain, and 3 to 4 km near Valyermo where initial uplift and compression are in progress. Between Table Mountain and Valyermo, deformation since 0.78 Ma has involved a series of time transgressive high-angle north-dipping reverse faults which were active during the local initiation of uplift. These faults became progressively less active as they were uplifted 1.0 to 1.6 km with growth of the northeast-dipping monocline. Thus, the reverse faults provide evidence for northwestward migration of localized compression adjacent and north of the San Andreas fault from Table Mountain to Valyermo. In addition, the Llano fault represents a steeply southwest dipping reverse fault that may also have exhibited northwest migrating time transgressive activity during the late Quaternary.

The northwest migrating compression and uplift adjacent to the San Andreas fault results from the interaction of the San Jacinto and Cucamonga fault zones with the San Andreas fault at depth. Specifically, the northward extension of the Perris Block is pushed below the San Gabriel Mountain block and collides with the San Andreas fault at a depth of 8 to 9 km beneath Table Mountain. Motion of the Perris Block is presumably parallel to the San Jacinto fault, which has a slightly convergent slip vector relative to the San Andreas fault of approximately 20 degrees. Thus, the Perris Block collides with the San Andreas fault between the northeastern San Gabriel Mountains and deflects it northward beneath Table Mountain resulting in a subsurface restraining bend. Due to motion across the San Andreas fault, the north-dipping subsurface restraining bend and lateral ramp migrated toward the northwest, producing a dynamic locus of compression and uplift in the rocks north of the San Andreas fault. Once the rocks achieved maximum uplift, they maintained their relatively high elevation without further deformation, suggesting that a lateral ramp exists behind the leading restraining bend.

Return to the Stop on Highway 138, I-15 crossing.

Proceed west on Hwy 138. Cross over railroad tracks and under the railroad trestle. The spectacular white arkosic hogbacks called Mormon Rocks are part of the Cajon Valley Beds, Unit 2. Geologists

Figure 10. Mormon Rocks, a hogback of steeply dipping Middle Miocene Cajon Valley beds, consisting of arkosic sandstones. initially thought that these arkose units were equivalent to similar-appearing sediments in the Devils Punchbowl Formation, to the west, at Valyermo. Both arkosic units sit unconformably on a marine formation that had been referred to the San Franscisquito. Woodburne and Golz (1972) pointed out the lithologic differences in the underlying marine formation, and the presence of an elasmosaur relegated the Cajon portion of those beds to a Cretaceous age (Lucas and Reynolds, 1991). Woodburne and Golz (1972) demonstrated that the age of the Devils Punchbowl arkose was late Miocene (Clarendonian– Hemphillian NALMA), while vertebrate fossils in the Cajon Valley beds were middle Miocene (Hemingfordian–Barstovian NALMA). Therefore these look-alike arkosic beds were probably deposited under similar conditions, but at intervals separated by at least five million years.

43.7 (1.3) Turn left on Lone Pine Canyon Road. Cross Swartout Canyon Road junction and continue along the Lone Pine Canyon Road.

Figure 11. Map of the Lone Pine Road and the Lytle Canyons, with landslides and other slope failures from Hazlett, 2001

Note the burnt chaparral vegetation from the October 2009 fires which postponed our annual field trip.

51.6(7.9) Entering Wrightwood. The road towards Wrightwood ascends the wide floor of Sheep Creek Valley, choked with debris and mudflows derived from the Wright Mountain Ridge, composed of weak Pelona Schist. The steepness of the Wright Mountain, combined with rapid transpressional uplift, associated with the Cucamonga thrust, and strike slip faulting at the base of the ridge, has resulted in spectacular debris flows, even visible in the satellite image, below.

Figure 12. Facing the Lone Pine Canyon, towards Wrightwood in the northwest. The San Andreas Fault zone is several hundred feet wide and the relatively flat valley floor is covered with low chaparral vegetation. (Photo by Vik Mathur)

The road towards Wrightwood ascends the wide floor of Sheep Creek Valley, choked with debris and mudflows derived from the Wright Mountain Ridge, composed of weak Pelona Schist. The steepness of the Wright Mountain, combined with rapid transpressional uplift, associated with the Cucamonga thrust, and strike slip faulting at the base of the ridge, has resulted in spectacular debris flows, even visible in the satellite image, below.

Figure 13. Satellite Image of the San Andreas Fault Zone and the Sheep Creek Debris Flow in the Wrightwood Area. The destructive debris flows occurred in 1941 and 1969 and involved Pelona Schist. (Satellite image from www.sanandreas.org)

52.1(0.5) Crossing the Sheep Creek Landslide Area. Note the greenish debris derived from Pelona Schist.

The Pelona Schist, in the Lone Pine Canyon, as through most of the Cajon Pass area, is very unstable. Pieces of actinolite bearing Pelona Schist are common in the debris where Lone Pine Canyon Road crosses the Sheep Canyon channel. Actinolite occurs as a metamorphic product of mafic rocks, with green schist and epidote-amphibolite facies. Today we encountered the Pelona Schist at the Blue Cut in Cajon Pass and tomorrow we will discuss its origin during our stop at Manker Flats and San Antonio Falls. Morton and Campbell (1989, p.174, in Hazlett, 2001), describe a three-stage cyclical behavior in the development of the landslide and the debris flows. “The three stages are independent, occur in sequence, and are of different duration. Deposits of the first stage, the largest in size, are removed to positions farther downstream by the activity of the second and third stage landslides.

Figure 14. Wrightwood Area debris flows, landslides and related control works (from Morton and Sadler 1989)

“First-stage landslides are represented by huge slumped masses derived from steep bedrock slopes in the canyon heads; the material moves down the principal stream drainage, which may be completely filled with debris. Second stage activity develops as streams cut a network of branching channels into the massive first stage deposit. The second-stage landslides are chiefly slumps from the other slide mass and from adjacent bedrock slopes. The movement of these slides is generally down slope toward actively eroding drainages. Third-stage activity includes mudflows that accompany the spring melting of snow pack. The debris moves down the stream channels to depositional reaches on major fans. Removal of sufficient amounts of first-stage events resets the bedrock slope of the main drainage for another first stage event.

“The first-stage landslides in the Wrightwood area are of prehistoric origin, and their recurrence interval in any canyon is probably several thousand years. Second-stage landslides last one to years and are apparently preceded and triggered by a series of high-precipitation sequences, ranging from a few days to as much as six weeks; peak mudflow activity apparently results when a heavy spring snow melt occurs during a period of second stage landslide activity.”

52.3 (0.2) Turn right on Sheep Creek Road, through the residential area of Wrightwood.

52.7 (0.4) Turn left on SR-2, going west. After leaving Wrightwood, we follow the Swartout Creek, along the San Andreas fault, past a ski area and the U.S. Forest Service Visitor’s Center.

57.3 (3.6) Junction of Hwy N4 and SR-2. Continue uphill on SR-2.

59.2 (1.9) Vista at Inspiration Point

Figure 15. Inspiration Point (Elev. 7386 ft.) Overlook in October 2009, with autumn colors of buckwheat and rabbit brush flowers. You are looking at the headwaters of the East Fork of the and San Gabriel River and the north face of the Mt. San Antonio (elev. 10,064 ft.), also known as Mt. Baldy.

59.8 (0.6) Grassy Hollow U.S. Forest Service Visitor’s Center LUNCH STOP.

STOP A6: VINCENT GAP AND GRASSY HOLLOW

Figure 16. Grassy Hollow Visitor Center Entrance, on a snowy day in April, 2010 (Photo by Vik Mathur)

62.5 (2.7) Vincent Gulch Divide Gate (Elev 6565 ft.)

63.6 (1.1) Stop A7.

STOP A7: SLOPE STABILITY PROJECT AT THE ANGELES HWY 2 BRIDGE

Field Presentation by Chris Goetz and Chris Harris; also see the Goetz and Harris article, this volume

The torrential rains and snowfall that struck Southern California during the winter of 2004-2005, resulted in extensive slope failures This caused the closure of SR-2, the Angeles Crest Highway, between Islip Saddle and Vincent Gap for over 4 years from December 2005 and May 2009. The roadway damage at this site occurred along a steep north facing slope which is underlain by gneissic bedrock that is partially covered by a discontinuous veneer of talus. The failure at Mile post (MP) 74.05 involved total loss of west bound shoulder and incipient cracking within the westbound lanes. Subsequent slope failure during the winter of 2006 later removed the eastbound lane as well. East of the site, there is a perennial creek that drains beneath the roadway in a 3-ft diameter corrugated metal pipe (CMP). A blockage of the CMP by the rock and wood debris likely caused storm runoff to overflow onto the roadway, resulting into the roadway failures. Based on the geological/geotechnical investigations, Caltrans elected to repair the roadway by constructing a bridge at MP 74.08 and by constructing the embankment, utilizing a geo-grid reinforced slope. Caltrans also improved drainage at the creek by adding two additional 2-ft. diameter CMPs beneath the roadway.

Figure 17. Slope Failure on SR-2, following the torrential rains of winter 2004-2005. The bedrock is Precambrian gneiss, exposed in 45-50 degree slopes (Photo from Goetz, URS).

Figure 18. Completed single-span SR-2 bridge, with roadway embankment and geo-grid reinforced slope, and improved drainage in the perennial stream below.

END OF THE DAY 1 FIELD TRIP. Day 2, Sunday, June 20, 2010.

Highlights: San Antonio Creek Watershed, Cow Canyon Saddle Landslide, US Forest Service Visitor’s Center, Igneous Dikes and 1938 Floods, Manker Flats and San Antonio Falls, 1969 Flood Terraces, and San Antonio Dam.

0.0 (0.0) Start at Cow Canyon Saddle at the entrance of Mt. Baldy Ranch R.V. Park, 30601 East Glendora Ridge Road, Mt. Baldy, CA 91759, driving down towards Mt. Baldy Village.

STOP B1: COW CANYON SADDLE OVERLOOK

Field Presentation by Jon Nourse

The valley to the west is controlled by at least three strands composing the north branch of the San Gabriel Fault zone. The fault recorded about 13 miles of right lateral slip between 12Ma and 5 Ma. To the east the San Gabriel fault is truncated by the San Antonio Canyon (SAC) fault, with a left lateral displacement of about 2 miles to Icehouse Canyon (Nourse and others, 1994). The intersection of the two faults is buried by the Cow Canyon Landslide.

Walk down the road, to the overlook facing east into the head scarps of the Cow Canyon landslide across the San Antonio Canyon. Along the road are the outcrops of the toe of the slide with distinct clasts of garnet-biotite quartz feldspar gneiss, quartzite, marble, calcsilicate gneiss and graphitic phyllite (Figure19, below).

Figure 19. Outcrop of the toe of the Cow Canyon Landslide, with clasts of gneiss, quartzite, marble and graphitic phyllite.

Return to the cars and drive down the Glendora Ridge Road.

Figure 20. San Antonio Canyon and the vicinity, with Day 2 field stops

0.8(0.8) Turn left onto Mt. Baldy Road and into Mt. Baldy Village

1.0 (0.2) Turn left into U.S. Forest Service Visitor’s Center STOP 2 STOP B2: USFS VISITORS’ CENTER

Field presentation by Carolyn Summers, instructor Environmental Education program

Gather around the campfire circle, with displays of the Tongva village and mining camp demonstrations

Figure 21. U.S. Forest Service Mt. Baldy Visitor Center compound, with displays of a Tongva Village and a Mining Camp, representative of past land use in the area.

Return to Mt. Baldy Road, turn left through the village.

1.2 (0.2) Buckhorn Lodge and the crossing of San Antonio Creek

1.4 (0.2) Park in the parking lot on the left, across from the trout ponds

STOP B3: GNEISS-DIKES INTRUSIONS AND 1938 FLOODS

Field presentations by Jon Nourse and Prem Saint

The Buckhorn Restaurant and Lodge, below, and the trout ponds are located at a site where the 1938

Figure 22. The Buckhorn Lodge today. From Osborne, 2005 flood destroyed a flourishing Camp Baldy Resort, operated by a member of the family of the Yosemite Camp Curry fame.

Figure 22. Historical Pictures of the Curry Mt. Baldy Lodge, destroyed by 1938 floods (from Osborne, 2005, A Guide to Mt. Baldy & San Antonio Canyon)

Walk down to the flood plain and the riparian zone of the San Antonio Creek. The creek contains boulders of diverse plutonic and metamorphic rocks, including those from the Telegraph Peak pluton which is the source of Late Oligocene rhyolite porphyry sills and dikes exposed in the outcrops to the west of the creek (Nourse and others, 1998). Cross the creek to examine the bedrock of the Precambrian gneisses with cross-cutting dikes and sills, (Figure 22). The gneiss bedrock represents some of the oldest rocks in California and were formed in a supercontinent called Rodinia, that existed between 1700 Ma and 800 Ma (Figure 24). Seventy mafic and intermediate dikes measured in this area cluster into two orientations: N45W/85NE and N80W/60NE. The younger dike swarm is disrupted by brittle faults with distinct orientations and styles. Younger, northeast-striking, northwest dipping faults that display prominent left lateral and oblique-sinistral reverse faults. The perennial flow of the San Antonio Creek provides a critical watering hole for wildlife, including the bighorn sheep (Figure 25)

Figure 23. Rhyolite Dikes and Sills intruded by younger mafic and intermediate dikes, all intruded into southwest dipping mylonites and Precambrian gneiss (Photo by Dee Trent).

Figure 24. Reconstruction of the Rodinian Landmass, a supercontinent that existed between 1700 Ma and 800 Ma, during which the Precambrian gneiss of the San Gabriel Mountains and the Joshua Tree Area was formed (from Trent and Hazlett, 2002)

Figure 25. Riparian Zone of the San Antonio Creek, along with the perennial streamflow provides an important watering hole for the wildlife, including the Bighorn sheep. Return to the cars and proceed north on Mt. Road. The road cut across from the parking lot exposes a part of the dissected Cow Canyon Landslide (Figures 26, 27, and 28), we met at the Cow Canyon Saddle, stop 1.

Figure 26. Outcrop of the Dissected Cow Canyon Landslide, east of the parking lot across from the trout

2.2 (0.8) Cross San Antonio Creek bridge with large boulders.

2.6 (0.4) Go past the Icehouse Canyon trailhead turnoff towards the Mt. Baldy Ski area, crossing several switchbacks with road cuts in another dissected landslide, the Mt. San Antonio Slide, with the source area in the between Mt. San Antonio and Mt. Harwood (Figure 27). Note the change in vegetation as we ascend beyond 500 ft. into various vegetation and habitat zones, from chaparral to the different Pine and Fir Communities (Figure 29).

Figure 27. Landslides and Debris Flows in the San Antonio Canyon (from Hazlett, 2001)

Figure 28. Geologic Map of the San Antonio Canyon in the vicinity of Mt. Baldy Village. From Dibblee, 2002.

Figure 29. Vegetation and Habitat Zones, as you drive up the Mt. Baldy Road from the foothills to the top of the Mt. San Antonio (Mt. Baldy), passing from chaparral to the the different pine and fir communities. Where there are perennial streams, like the Icehouse Creek and San Antonio Creek, locally these zones are interspersed with riparian zones.

5.0 (2.4) Manker Flats, with mounds of mine tailings containing Pelona Schist (Figure 30), a reminder of hydraulic mining for gold in the Mt. Baldy Notch Area that date back to 1880s and 1890s (Trent, 2001).

5.7. (0.7) Park in the parking lot at the intersection of Manker Flats and San Antonio Falls Road, display the US Forest Service Day Parking Pass inside your winshield and walk up the USFS fire road towards the San Antonio Falls.

Figure 30. Manker Flats with mine tailings containing Pelona Schist and other rocks, a remnant of hydraulic gold mining in Mt. Baldy notch area.

Figure 31. Geological Map of the Manker Flats, San Antonio Falls and the Baldy Notch (from Diblee 2002) STOP B4. MANKER FLATS AND SAN ANTONIO FALLS

Field Presentation by Jonathan Nourse

Walk up road through a west-dipping section of Pelona schist that composes the footwall of the Vincent thrust. These rocks were first mapped in detail by Perry Ehlig (1958) as part of his doctoral dissertation. Greenschist, grayschist, and quartzite derived from mafic igneous rocks, graywacke/mudstone, and chert, respectively, is strongly sheared and transposed. These oceanic rocks were overthrust by San Gabriel continental basement during late Mesozoic-Early Cenozoic time (Ehlig, 1981; Nourse, 2002; Dibblee, 2003). Notice the complex mesoscopic folds, especially well-preserved in metachert layers. Along this stretch of the road, the metamorphic fabrics are intruded by several rhyolite porphyry dikes and one mafic dike. From the first switchback (0.6 mi above the gate) is a spectacular view of San Antonio Falls (Figure 32). These waterfalls in upper San Antonio watershed provide a beautiful

Figure 32. San Antonio Falls with their water source Figure 33. Pelona Schist outcrop on the Mt. Baldy in a line of springs located above 8200 feet. Note fire Road, with rhyodacite porphyry dikes and sills, the exposures of Pelona Schist with rhyodacite sills cut by reverse faults, indicating a local and dikes. accommodation for transpressional forces (photo by Trent, 2001) illustration of local hydrology and geology. The primary water source for San Antonio Creek is a line of springs located upstream at 8200ft elevation, just above Sierra Hut. At Sierra Springs, water contained in a porous talus boulder slope (Baldy Bowl) is forced to the surface along a lower boundary with impermeable rock (Pelona schist). Water passing over San Antonio Falls (elevation 6400 ft) is joined downstream by flow from Manker springs and Icehouse Creek. Farther downstream San Antonio Creek supplies water to residents of Mt. Baldy village and Upland. Hydroelectric power is also generated as the creek drops 1660ft elevation between the Mt. Baldy village and San Antonio Dam. The cliffs before you reveal rock layers that have been carved and exposed by the erosive action of San Antonio Creek. In detail, these rocks compose two contrasting packages separated by the Vincent thrust (a fault named for its exposure near Vincent Gap). The Vincent thrust marks a major tectonic collision zone between an ancient continent and an adjacent ocean basin. Perry Ehlig (1927-1999) was first to map this fault in detail during the 1950s as part of his PhD dissertation. Perry walked virtually every inch of the Vincent thrust, a significant accomplishment in this rugged, dense chaparral country (Figure 34). The gray rocks

Figure 34. Rugged, dense chaparral vegetation, covering the exposures of Vincent Thrust in the Eastern San Gabriel Mountains. exposed in the lower part of the falls are metamorphosed sands, silts, and muds, originally deposited in a deep ocean basin about 80 Ma. The green layers represent metamorphosed basaltic lavas that erupted within this ocean basin. The Vincent thrust is exposed just above the prominent tree-covered ledge to the upper left of San Antonio Falls. The steep cliffs above the Vincent thrust contain rocks of continental origin ranging in age from about 1700 to 80 Ma. Samples of these rocks may be viewed in the talus slope to the left of the falls. Especially noticeable is a distinct white rock with large black crystals informally named “dalmationite” by Ehlig. This igneous rock crops out along with a finer grained black and white quartz diorite near the summit of Mt. San Antonio. Close inspection of the waterfall outcrop reveals uniformly dipping Pelona schist intruded by two prominent rhyodacite porphyry sills, in turn cut by thinner mafic-intermediate dikes. Several northeast-striking faults disrupt the continuity of the rhyodacite sills. Apparent left lateral and/or reverse displacements are compatible with more accessible exposures observed farther up San Antonio Falls Road. Follow a narrow trail to the base of the falls. A somewhat treacherous scramble up the talus slope south of the falls will afford up-close examination of the intrusive relationships. The road climbs another 3 mi to Mt. Baldy Notch, during which it crosses the San Antonio Canyon Fault four times as it bends from a N30E to N80E strike. Brittle strain near this fault appears to be partitioned into reverse and sinistral components to accommodate local transpression. For example, near Manker Creek crossing (1.4 to 1.7 mi above the gate), about 300 m northwest of the San Antonio fault), rhyolite porphyry sills in Pelona schist are offset by a family of reverse faults. Differential movements between reverse faults (see also Figure 2-8 of Trent and Nourse, 2001) have rotated schist foliations to steep southwest dips and resulted in moderate northeast dips for two mafic- intermediate dikes. One mafic dike exposed 120 m up Manker Creek displays significant sinistral offsets. Farther up the road (2.8 mi past the gate) the main trace of the San Antonio fault is exposed beneath the ski lift Kinematic features here indicate pure left-lateral movements

Figure 35. Upper San Antonio Creek Watershed Map with springs and headwaters above Manker Flats and San Antonio Falls (from CalPoly, Pomona, Senior Thesis.)

Return to your car in the Manker Flats Parking Area.

5.7 (0.5) The Snowcrest Inn is on the right, continue driving south

7.7 (2.0) Drive past the turnoff for the Icehouse Canyon Road.

9.0. (1.3) Cross San Antonio Creek bridge at Buckhorn Lodge parking area.

9.4.(0.4) Glendora Ridge Road turnoff on right. Continue south on the Mt. Baldy Road, passing road cuts with landslide deposits from the Hogback Landslide (Figures 36 and 37).

Figure 36. Hog Back Landslide Map showing the head scar and the toe intercepted by Mt. Baldy Road (map from Herber, 1987).

13.9(4.5) Turn left on Shinn Road, going towards San Antonio Heights

14.2. (0.3) Cross San Antonio Creek and park across from the USForest Service Fire Station, on the terrace of the San Antonio Creek.

Figure 37. Cross-Section across Hog Back Figure 38. San Antonio Creek during the1969 Landslide from A-A’, by Herber 1987. Floods at Shinn Road crossing area (Photo from USFS)

STOP B5: 1969 FLOOD TERRACES AND SAF OUTCROP

Field presentation by Jon Nourse.

Figure 39. San Antonio Creek in the vicinity of Shinn Road, with terraces, alluvial scrub, and riparian vegetation consisting of willows and other phreatophytes.

Figure 40. Geologic Map of San Antonio Dam Area, showing the location of faults at Stops A5 and A6. (Map from Diblee, 2002). Return to your car and to Mt. Baldy Road stop, staying in the left lane. Turn left on Mt. Baldy Road.

15.6 (1.4) Park on the left into the parking area overlooking the San Antonio Dam

Figure 41. U.S. Army Corps of Engineers Sign at San Antonio Dam overlook, detailing the dam statistics.

STOP B6: SAN ANTONIO DAM OVERLOOK

Field Presentation by Jon Nourse (Notes from Nourse, 2003)

Also see Diblee Map, Figure 40, for field relationships.

San Antonio Dam (Figure 41) was built by the Army Corps of Engineers in 1956 to prevent a repeat of the high waters that inundated Upland, Claremont, and La Verne during March of 1938. It played a crucial role in reducing damage during the 1969 flood. In addition to flood control, the dam also serves the purpose of groundwater recharge. Its porous and permeable substrate supplies renewable well water to the City of Upland. San Antonio reservoir has never exceeded the height of the spillway, but its water elevation reached 2193 ft and 2226 ft during January of 1969 and February of 1980, respectively (Figure 42).

The earth-fill design of San Antonio Dam (Figure 43) is prudent given its location near the intersection of three active faults that conceivably might rupture a concrete structure. The dam is positioned across an apparent left-lateral deflection or tear in the Sierra Madre-Cucamonga thrust. Coinciding with this deflection is a prominent left-step between the San Antonio Canyon fault and the inferred northeast projection of the San Jose fault (Herber, 2001). Given that both of these latter structures record left- lateral displacements, the fault geometry suggests that the thick alluvium beneath San Antonio reservoir occupies a pull-apart basin.

Figure 42: Hydrograph of San Antonio Creek Flow through San Antonio Dam, as gaged by the U.S> Army Corps of Engineers, from 1958‐2003 (from Nourse, 2009)

Figure 43. Geologic Cross-section across San Antonio Dam, with personal notes by Professor Larry Herber, 2001, Geology Department, CalPoly, Pomona.

The epicenter of the 1990 magnitude 5.4 Upland earthquake was directly south of San Antonio Dam (Hauksson and Jones, 1991). This earthquake and a similar event in 1988 (M=4.5) are believed by these authors to have ruptured the San Jose fault. Detailed analysis of the 1990 Upland event and its aftershocks indicates left-lateral oblique reverse displacement on a fault with an orientation of N26E/77NW (Dreger and Helmberger, 1990). Rupture initiated at a depth of 6 km.

The Sierra Madre-Cucamonga fault has not ruptured in the immediate vicinity during historical time. However, the entire frontal fault system is classified as active and capable of generating a magnitude 7 earthquake (Dolan et al., 2005). Its youthfulness is implied by prominent escarpments along the range front, and evidence for accelerated erosion that we will view later today. Also, both the east and western abutments of San Antonio Dam preserve dramatic examples of north-dipping thrust faults that break crystalline rocks. These faults, synthetic to the modern-day Sierra Madre-Cucamonga thrust, have facilitated uplift of the eastern San Gabriel Mountains. There is an active sand and gravel quarry operations as shown in Figure 44.

Figure 44. San Antonio Earthfill Dam, in April 2010, with a partial-filled reservoir and access roads for sand and gravel operations

The spillway is now the site of a lot of grafitti, or urban artwork. So, we’ll end the trip for you to enjoy an expression of local urban creativity. END OF THE TRIP.

LITERATURE CITED & SELECTED BIBLIOGRAPHY

Acosta, R. G., Heise, R. C., and Nourse, J. A., 1998, Syntectonic sedimentation within the San Jacinto Fault Zone as Recorded by the Eastern Borrego Badlands, California: Geological Society of America Abstracts with Programs, v. 30, no. 5, p. 2.

Agunwah, Reggie, 2009, Structural Analysis of Oriented Blocks in the Hogback Landslide Deposit, Eastern San Gabriel Mountains, California: senior thesis, Cal Poly Pomona, 21 pages plus attachments.

Allen, C. R., 1957, San Andreas Fault Zone in San Gorgonio Pass, Southern California: Bulletin of the Geological Society of America, vol. 68, p. 315-350.

Atwater, T., 1970, Implications of plate tectonics for the Cenozoic tectonic evolution of western North America: Geological Society of America Bulletin, v. 81, p. 3513-3535.

Barnes, L. G., and R. E. Reynolds, 2007. A primitive early Miocene platanistoid dolphin (Cetacea: Odontoceti) from Cajon Pass, San Bernardino County, California. Proceedings of the 2007 Desert Research Symposium, California State University, Fullerton, p. 107.

Barrows, A. G., Kahle, J. E., and Beeby, D. J., 1985, Earthquake hazards and tectonic history of the San Andreas Fault Zone, Los Angeles County, California: California Department of Conservation, California Division of Mines and Geology, Open File Report 85-10, pp. 139.

Barth, A. P., Tosdal, R. M., and Wooden, J. L., 1990, A petrologic comparison of Triassic plutonism in the San Gabriel and Mule Mountains, southern California: Journal of Geophysical Research, v. 95, n. B12, p. 20,075-20,096.

Crook, R., Jr., Allen, C. R., Kamb, B., Payne, C. M., and Protor, R. J., 1987, Quaternary geology and seismic hazard of the Sierra Madre and associated faults, western San Gabriel Mountains, in Morton, D. M., and Yerkes, R. F., eds., Recent Reverse Faulting in the Transverse Ranges, California, p. 27-63.

Crowell, J. C., 1975, The San Gabriel fault and Ridge basin, southern California, in Crowell, J. C., ed., San Andreas fault in southern California: California Division of Mines and Geology Special Report 118, p. 208-218.

Crowell, J. C., 1975, The San Gabriel Fault and Ridge Basin, southern California: in Crowell, J.C., ed., San Andreas Fault in Southern California: California Division of Mines and Geology Special Report 118, p. 208-219 Crowell, J. C., 1981, An outline of the tectonic history of Southern California, in Ernst, W. G., ed., The geotectonic development of California; Ruby Volume 1: Englewood Cliffs, New Jersey, Prentice-Hall, p. 583-599.

Dibblee, T. W. Jr. 1967. Areal geology of the western Mojave Desert. U. S. Geological Survey Professional Paper 522:1-53.

Dibblee, T. W. Jr., 1967, Areal geology of the western Mojave Desert, California: U.S. Geological Survey Professional Paper 522, p. 153.

Dibblee, T. W., Jr., 2002, Geologic map of the Mt. Baldy quadrangle, Los Angeles and San Bernardino Counties, California: Dibblee Geological Foundation Map DF-90.

Dibblee, T. W., Jr., 2003, Tectonic genesis of the San Gabriel Mountains, in Weigand, P. W. ed., Late Cenozoic magmatism, faulting, uplift, flooding, and erosion in the eastern San Gabriel Mountains and Pomona Valley (field trip guidebook): Dibblee Geology Center, p. 1-41.

Dickinson, W. R., 1996, Kinematics of transrotational tectonism in the California Transverse Ranges and its contribution to cumulative clip along the San Andreas Transform Fault System: Geological Society of America, Special Paper 305, p. 46

Dolan, J. F., 1995, Prospects for larger or more frequent earthquakes in the greater Los Angeles region, Science, v. 267, Issue 5195, p. 199-205.

Dreger, D.S. and Helmberger, D.V., 1990, Broadband modeling of local earthquakes, Bulletin of the Seismological Society of America, v. 80, n. 5, p. 1162-1179

Ehlig, P. L., 1958, Geology of the Mt. Baldy region of the San Gabriel Mountains: Ph.D. thesis, University of California, Los Angeles, 192 p.

Ehlig, P. L., 1975, Basement Rocks of the San Gabriel Mountains, South of the San Andreas Fault, southern California: in Crowell, J.C., ed., San Andreas Fault in Southern California: California Division of Mines and Geology Special Report 118, p. 177-186.

Ehlig, P. L., 1981, Origin and tectonic history of the basement terrane of the San Gabriel Mountains, central Transverse Ranges, in Ernst, W. G., ed., The Geotectonic Development of California: Englewood Cliffs, NJ, Prentice-Hall, p. 254-283.

Ehlig, P. L., 1981, Origin and tectonic history of the basement terrane of the San Gabriel Mountains, central Transverse Ranges, in Ernst, W. G., ed., The geotectonic development of California; Ruby Volume 1: Englewood Cliffs, New Jersey, Prentice-Hall, p. 253-283. Ehlig, P. L., and Dillon, J. T., 1993, Displacement on the southern San Andreas Fault: in Powell, R. E., Weldon, R. J., II, and Matti, J. C., eds., The San Andreas Fault System: Displacement, Palinspastic Reconstruction, and Geologic Evolution: Boulder, Colorado, Geological Society of America, Memoir 178. p. 199-216.

Foster, J. H. 1980. Late Cenozoic tectonic evolution of Cajon Valley, southern California. PhD dissertation, Department of Geological Sciences, University of California, Riverside, California, 238 pp.

Foster, J. H., 1980, Late Cenozoic Tectonic Evolution of Cajon Valley, Southern California: [Ph.D. Thesis], University of California Riverside, 242 pages.

Foster, J. H., 1982, Late Cenozoic tectonic evolution of Cajon Valley, southern California, in Cooper, J. D., compiler, Geologic excursions in the Transverse Ranges: Geological Society of America, Cordilleran Section Field Trip Guidebook 6.

Frizzell, V. A. Jr., Mattinson, J. M., and Matti, J. C., 1986, Distinctive Triassic megaprophyritic monzogranite: Evidence for only 160 km offset along the San Andreas Fault, southern California: Journal of Geophysical Research, Vol. 91, No. B14, p.14080-14088.

Hauksson, E. and Jones, L., 1991, The 1988 and 1990 Upland earthquakes: Left-lateral faulting adjacent to the central Transverse Ranges, Journal of Geophysical research, v. 96, n. B5, p. 8143-8165

Heaton, Daniel, 2008, Comparison of Late Cretaceous plutonic rocks across the San Antonio Canyon fault, San Gabriel Mountains, California: senior thesis, Cal Poly Pomona, 23 pages.

Herber, L. J., 1987, Hog Back: A grossly stable prehistoric translatory rock block slide, San Antonio Canyon, southern California: Geological Society of America Centennial Field Guide— Cordilleran Section, p. 201-202.

Herber, L. J., 1998, San Antonio Canyon: Cultural geography, Late Cenozoic geology, geomorphology, and environmental geology of an alpine valley in southern California, in R. J. Behl, ed., Field trip Guidebook for the Cordilleran Section GSA meeting, Long Beach, California, p. 3.1-3.21.

Herber, L. J., 2001, Selected environmental geology features of the lower San Antonio Canion and San Antonio Heights areas, in Hazlett, R. and Trent, D, eds., San Antonio Canyon, Mount San Antonio, Cajon Pass, and Wrightwood areas, southern California: Field Trip Guidebook for NAGT Far Western Sectional meeting, Pomona College, p. 2.1-2.16.

Hill, M. L., and Dibblee, T. W., Jr., 1953, San Andreas, Garlock, and Big Pine faults, California: A study of the character, history, and tectonic significance of their displacement: Geological Society of America Bulletin, v. 64, p. 443-458. Humphreys, E. D., and Hager, B. H., 1990, A kinematic model for the late Cenozoic development of southern California crust and upper mantle: Journal of Geophysical Research, v. 95, n. B12, p. 19,747-19,762.

Humphreys, E.D., 1995, Tectonics of the Greater Los Angeles Region: Implications for the lower crust and upper mantle: American Geophysical Union EOS, vol, 76, no. 46, p. F347.

Jacobson, C. E., Barth, A. P., Grove, M., Nourse, Jonathan A., 2004, Detrital zircon geochronology indicates that Upper Cretaceous to Eocene sedimentary and metasedimentary rocks of southern California, Salinia, and the Sur-Obispo terrane are not far traveled, Geological Society of America Abstracts with Programs, v. 36, n. 5, p.

Joseph, S. E., Davis, T. E., Ehlig, P. L., 1982, Strontium isotopic correlation of the La Panza Range granitic rocks with similar rocks in the central and eastern Transverse Ranges, in Fife D. L., and Minch, J. A., eds., Geology and Mineral Wealth of the California Transverse Ranges; Mason Hill Volume: Santa Ana, California, South Coast Geological Society Annual Symposium and Guidebook 10, p. 310-320.

Kenney, M. D., and Weldon, R. J., 1996a, Deformation of Table Mountain in the northeastern San Gabriel Mountains, southern California: Geological Society of America Abstracts with Programs, v. 28, no. 5, p.81.

Kenney, M. D., and Weldon, R. J., 1996b, A subsurface restraining bend in the Mojave segment of the San Andreas Fault, northeastern San Gabriel Mountains, California [abs.]: American Geophysical Union, Supplement to EOS, v. 77, no. 46, p. F743.

Kenney, M. D., and Weldon, R. J., 1998, Geologic Map: Mescal Creek 7.5-minute quadrangle, Northeastern San Gabriel Mountains, San Bernardino and Los Angeles Counties, Southern California: Geological Society of America Abstracts with Programs, v. 30, No. 5, p.23.

Kooser, M. A., 1980, Stratigraphy and sedimentology of the San Francisquito Formation, Transverse Ranges, California [Ph.D. thesis]: Riverside, California, University of California, p. 201.

Kooser, M.A. 1985. Paleocene Plesiosaur? In Geologic investigations along Interstate 15, Cajon Pass to Manix Lake, ed. R.E. Reynolds, 43-48. Redlands: San Bernardino County Museum.

Lindsay, E. H., and R.E. Reynolds, 2008. Heteromyid rodents from Miocene faunas of the Mojave Desert, Southern California; pp.213-235, in X. Wang and L. G. Barnes (eds.), Geology and vertebrate paleontology of western and southern North America, contributions in honor of David P. Whistler, Natural History Museum of Los Angeles County Science Series 41:i-viii, 1-388. Lucas, S.G. and R.E. Reynolds. 1991. Late Cretaceous (?) plesiosaurs from Cajon Pass, California. In Inland Southern California: the last 70 million years, ed. M.O. Woodburne, R.E. Reynolds, and D.P. Whistler, 52-53. Redlands: San Bernardino County Museum Association Quarterly 38(3,4).

Matti, J. C., Frizzell, V. A., and Mattinson, J. M., 1986, Distinctive Triassic megaporphyritic monzogranite displaced 160 +/- 10 km by the San Andreas Fault, southern California: A new Constraint for Palinspastic Reconstructions: Geological Society of America Abstracts with Programs, v. 18, p.154.

Matti, J. C., Morton, D. M., 1993, Paleogeographic evolution of the San Andreas Fault in southern California: A reconstruction based on a new cross-fault correlation, in Powell, R.E., Weldon, R.J., II, and Matti, J.C., eds., The San Andreas Fault System: displacement, palinspastic reconstruction, and geologic evolution: Boulder, Colorado, Geological Society of America, Memoir 178, p. 107-159.

Matti, J. C., Morton, D. M., and Cox, B. F., 1985, Distribution and geologic relations of fault systems in the vicinity of the central Transverse Ranges, southern California: U.S. Geological Survey Open- File Report 85-865, p. 27.

May, D. J., and Walker, N. W., 1989, Late Cretaceous juxtaposition of metamorphic terranes in the southeastern San Gabriel Mountains, California: Geological Society of America Bulletin, v. 101, p. 1246-1267.

May, S. R., and Repenning, C. A.,1982, New evidence for the age of the Old Woman Sandstone, Mojave Desert, California, in Cooper, J.D., compiler, Geologic Excursions in the Transverse Ranges, southern California: Geological Society of America, Cordilleran Section Annual Meeting Volume and Guidebook: Fullerton, California State University Department of Geological Sciences, p. 93-96

McFadden, L. D., and Weldon, R. J., 1987, Rates and processes of soil development on Quaternary terraces in Cajon Pass, California: Geological Society of America Bulletin, v.98, p. 280-293.

Meisling, K. E., 1984, Neotectonics of the north frontal fault system of the San Bernardino Mountains: Cajon Pass to Lucerne Valley, California, [Ph.D. thesis]: Pasadena, California, California Institute of Technology, p. 394

Meisling, K. E., and Weldon, R. J., 1989, Late Cenozoic tectonics of the northwestern San Bernardino Mountains, southern California: Geological Society of America Bulletin, v.101, p.106-128.

Meisling, K.E., and R .J. Weldon. 1982. The late Cenozoic structure and stratigraphy of the western San Bernardino Mountains. In Geologic excursions in the Transverse Ranges, southern California, ed. J.D. Cooper, 75-82. 78th Annual Meeting, Cordilleran Section, Geological Society of America.

Meisling, K.E., and R .J. Weldon. 1989. Late Cenozoic tectonics of the northwestern San Bernardino Mountains, southern California. Geological Society of America Bulletin 101:106-128.

Miller F. K., 1987, Reverse-fault system bounding the north side of the San Bernardino Mountains: U. S. Geological Survey Professional Paper 1339, p. 83-95

Morton, D. M., and Matti, J. C., 1993, Extension and contraction within an evolving divergent strike-slip fault complex: The San Andreas and San Jacinto Fault Zones at their convergence in southern California, in Powell, R.E., Weldon, R.J., II, and Matti, J.C., eds., The San Andreas Fault System: displacement, palinspastic reconstruction, and geologic evolution: Boulder, Colorado, Geological Society of America, Memoir 178, p. 217-230.

Morton, D.M., and F.K Miller. 2003. Preliminary geologic map of the San Bernardino 30´×60´ quadrangle, California: U.S. Geological Survey Open-File Report 03–293, http://geopubs.wr.usgs.gov/open-file/of03-293/. accessed 04/09/2008

Morton, D.M., and Miller, F.K. 2003, Preliminary geologic map of the San Bernardino 30’ x 60’ quadrangle, California: U.S. Geological Survey Open-File Report 03-293.

Morton, D.M., Sadler, P.M., Minnich, R.A, 1987, Large rock-avalanche deposits: examples from the central and eastern San Gabriel Mountains of southern California. Inland Geological Society, Volume 2, Part III, p. 20-31.

Neville, S. L., and Chambers, J. M., 1982, Late Miocene alkaline volcanism, northeastern San Bernardino Mountains and adjacent Mojave Desert, in Cooper, J.D., compiler, Geologic Excursions in the Transverse Ranges, southern California: Geological Society of America, Cordilleran Section Annual Meeting Volume and Guidebook: Fullerton, California State University Department of Geological Sciences, p. 103-106.

Noble, L. F., 1954, The San Andreas Fault Zone from Soledad Pass to Cajon Pass, California: California Division of Mines and Geology Bulletin, v. 170, p. 32-48.

Nourse, J. A., Hazelton, G. B., and Jones, R. K., 1994, Evidence for two phases of late Cenozoic sinistral displacement on the San Antonio Canyon fault, eastern San Gabriel Mountains, California: Geological Society of America Abstracts w/ Programs, p. 77.

Nourse, Jonathan A., 1999, Early-mid Miocene brittle structures and dikes in the San Gabriel Mountains prepare the ground for San Gabriel fault displacement, GSA Abstracts with Programs, v. 31, no. 2, p. A-155. Nourse, Jonathan A., 2002, Mid-Miocene reconstruction of the central and eastern San Gabriel Mountains, with implications for evolution of the San Gabriel fault and Los Angeles basin, in Barth, A. P. (ed.), Contributions to Crustal Evolution of the Southwestern United States, Boulder, Colorado: Geological Society of America Special Paper No. 365, p. 161-185.

Nourse, Jonathan A., 2003, Late Cenozoic Magmatism, Faulting, Uplift, Flooding, Erosion in the Eastern San Gabriel Mountains and Pomona Valley, in Weigand, P. W. (ed.), A Day in the Field With Tom Dibblee, Field Trip Guidebook published by the Thomas W. Dibblee, Jr. Foundation, May 24.

Nourse, Jonathan A., Morton, D.M., and Matti, J.C., 1998, Geologic map of the Mt.Baldy quadrangle, San Gabriel Mountains, California; United States Geological Survey Open File Report 98-BDY.

Nourse, Jonathan A., Weigand, Peter W., and Hazelton, Garrett B., 1998, Igneous and tectonic response of the eastern San Gabriel Mountains to Neogene extension and rotation of the Transverse Ranges block, in Behl, R. J., (ed.), Field Trip Guidebook for the 94th Annual GSA Cordilleran Section Meeting, CSU Long Beach, p. 10-1--10-15.

Nourse, Jonathan, 2003. A Day in the Field with Tom Diblee, Field Trip Notes from Dibblee Foundation

Oberlander, T. M., 1972, Morphogenesis of granitic boulder slopes in the Mojave Desert, California: Journal of Geology, v. 80, p. 1-20.

Osborne, Willis, 2005. A Guide to Mt. Baldy and San Antonio Canyon, self published.

Powell, R. E., 1993, Balanced palinspastic reconstruction of pre-late Cenozoic paleogeology, southern California: Geologic and kinematic constraints on evolution of the San Andreas fault system, in Powell, R.E., Weldon, R.J., II, and Matti, J.C., eds., The San Andreas Fault System: displacement, palinspastic reconstruction, and geologic evolution: Boulder, Colorado, Geological Society of America, Memoir 178, p. 1-106.

Powell, R. E., and Weldon, R. J., 1992, Evolution of the San Andreas Fault: Annu. Rev. Earth Planet. Sci., v. 20, p. 431-468.

Prentice C. S., and Weldon, R. J., 1986, Distribution of slip between the San Andreas and San Jacinto faults, near San Bernardino, southern California: Geological Society of America Abstracts with Programs, v. 18, p. 172.

Reynolds, R. E, 1985, Tertiary small mammals in the Cajon Valley, San Bernardino County, California: in Reynolds, R. E., ed., Geologic investigations along Interstate 15, Cajon Pass to Manix Lake, California: Western Association of Vertebrate Paleontologists Field Trip Guidebook, 60th Meeting. Redlands , California, San Bernardino County Museum, p. 49-58. Reynolds, R. E. 1984. Miocene faunas in the lower Crowder Formation, California: a preliminary discussion. In San Andreas Fault, Cajon Pass to Wrightwood, ed. R. L. Hester and D. E. Hallinger, 17-22. American Association of Petroleum Geologists, Pacific Section.

Reynolds, R. E., 1984, Miocene faunas in the lower Crowder Formation, Cajon Pass, California. A preliminary discussion: in Hester, R. L., and Hallinger, D. E., eds., San Andreas fault, Cajon Pass to Wrightwood: American Association of Petroleum Geologists, Pacific Section, Volume and Guidebook no 55, p. 17-21.

Reynolds, R.E. 1985. Tertiary small mammals in the Cajon Valley, San Bernardino County, California. In Geologic investigations along Interstate 15, Cajon Pass to Manix Lake, California, ed. R.E. Reynolds, 49-58. Redlands: San Bernardino County Museum.

Reynolds, R.E. 1991. Biostratigraphic relationships of Tertiary small vertebrates from Cajon Valley, San Bernardino County, California. In Inland Southern California: the last 70 million years, ed. M.O. Woodburne, R.E. Reynolds, and D.P. Whistler, 54-59. Redlands: San Bernardino County Museum Association Quarterly 38(3, 4).

Reynolds, R.E., R.L. Reynolds, and E.H. Lindsay. 2008. Biostratigraphy of the Miocene Crowder Formation, Cajon Pass, southwestern Mojave Desert, California; pp.237-253, in X. Wang and L. G. Barnes (eds.), Geology and vertebrate paleontology of western and southern North America, Contributions in honor of David P. Whistler, Natural History Museum of Los Angeles County Science Series 41:i-viii, 1-388.

Rogers, David J., Herber, Lawrence J., and Hibner, Thomas H., 1992, Paleolandslides in San Antonio Canyon, Eastern San Gabriel Mountains, California, in Pipkin, B. W. and Proctor, R. (eds.), Engineering Geology Practice in Southern California, American Association of Engineering Geologists, Star Publishing Co., p. 579-594.

Ross, D. C., 1972, Petrographic and chemical reconnaissance study of some granitic and gneissic rocks near the San Andreas Fault from Bodega Head to Cajon Pass, California: U.S. Geological Survey, Professional Paper 698, p. 92.

Sadler, P. M., 1993, The Santa Ana basin of the central San Bernardino Mountains: evidence of the timing of uplift and strike slip relative to the San Gabriel Mountains, in Powell, R. E., Weldon, R. J., II, and Matti, J. C., eds., The San Andreas Fault System: displacement, palinspastic reconstruction, and geologic evolution: Boulder, Colorado, Geological Society of America, Memoir 178, p. 307 - 321.

Sharp, R. V., 1967, The San Jacinto Fault Zone in the Peninsular Ranges of Southern California: Geological Society of America Bulletin, v. 78, p. 705-730. Shreve, R. L., 1959, Geology and mechanics of the Blackhawk landslide: [Ph.D. Thesis], Pasadena California, California Institute of Technology.

Silver, L.T., 1971, Problems of crystalline rocks of the Transverse Ranges: Geological Society of America Abstracts with programs, v. 3, p. 193-194.

Spotila, J. A., Farley, K. A., and Sieh, K., 1998, Uplift and erosion of the San Bernardino Mountains associated with transpression along the San Andreas fault, California, as constrained by radiogenic helium thermochronometry: Tectonics, v. 17, p. 360 - 378.

Trent, D. D, 2001, Geology, of the Mount San Antonio-Mount Harwood summit region, San Gabriel Mountains, California, in Hazlett, R. and Trent, D, eds., San Antonio Canyon, Mount San Antonio, Cajon Pass, and Wrightwood areas, southern California: Field Trip Guidebook for NAGT Far Western Sectional meeting, Pomona College, p. 4.1-4.9.

Trent, D. D., and Nourse, J. A., 2001, Geology, hydrology, and mining history of upper San Antonio Canyon, in Hazlett, R. and Trent, D, eds., San Antonio Canyon, Mount San Antonio, Cajon Pass, and Wrightwood areas, southern California: Field Trip Guidebook for NAGT Far Western Sectional meeting, Pomona College, p. 3.1-3.48.

Trent, D. D., Hazlett, R. W., and Nourse, J. A., 2001, Geology, of the Icehouse Canyon area, San Gabriel Mountains, California, in Hazlett, R. and Trent, D, eds., San Antonio Canyon, Mount San Antonio, Cajon Pass, and Wrightwood areas, southern California: Field Trip Guidebook for NAGT Far Western Sectional meeting, Pomona College, p. alt.4.1-alt 4.8.

Trent, Dee and Hazlett, Richard, 2002. Joshua Tree National Park Geology. Joshua Tree National Park Association

Walls, C., Rockwell, T., Mueller, K., Bock, Y., Williams, S., Pfanner, J., Dolan, J., and Fang, P., 1998, Escape tectonics in the Los Angeles Metropolitan Region and Implications for Seismic Risk: Nature, v. 394, n. 6691, p. 356-360

Weaver, C. E., 1951-56. Field notes on Paleocene in California, Pomona, Unpublished field notes, book 12, 252p.

Weldon, R. J. 1984. Implications of the age and distribution of the late Cenozoic stratigraphy in Cajon Pass, southern California. In San Andreas Fault, Cajon Pass to Wrightwood, ed. R. L. Hester and D. E. Hallinger, 9-16. Pacific Section, American Association of Petroleum Geologists.

Weldon, R. J. 1985. Implication of the age and distribution of the late Cenozoic stratigraphy in Cajon Pass, southern California. In Geologic investigations along Interstate, 15, Cajon Pass to Manix Lake, ed. R.E. Reynolds, 59-68. Redlands: San Bernardino County Museum. Weldon, R. J., 1981, Climatic control for the formation of terraced in Cajon Creek, southern California: Geological Society of America Abstracts with Programs, v. 15, p. 429.

Weldon, R. J., 1984a, Implications of the age and distribution of the Late Cenozoic stratigraphy in Cajon Pass, southern California: in, Hester, R. L. and Hallinger, D. E., eds., guidebook for the San Andreas Fault - Cajon Pass to Wrightwood: Annual Pacific Section American Association of Petroleum Geologists, v. 55, p. 9-15.

Weldon, R. J., 1984b, Quaternary deformation due to the junction of the San Andreas and San Jacinto Faults, southern California: Geological Society of America Abstracts with Programs, Cordilleran Section, v. 16, no. 6, p. 689.

Weldon, R. J., Humphreys, E., 1986, A kinematic model of southern California: Tectonics, v. 5, p. 33- 48.

Weldon, R. J., II, 1986, The Late Cenozoic Geology of Cajon Pass, Implications for Tectonics and Sedimentation along the San Andreas Fault: [Ph.D. Thesis], Pasadena California, California Institute of Technology, 400 pages including 12 unpublished map plates.

Weldon, R. J., Meisling, K. E., Allen, C. R., and Sieh, K. E., 1981, Neotectonics of the Silverwood Lake area, San Bernardino County: report to the California Department of Water Resources, pp. 22.

Weldon, R. J., Winston, D. S., Kirschvink, J. L., and Burbank, D. W., 1984, Magnetic stratigraphy of the Crowder Formation, Cajon Pass, southern California: Geological Society of America abstracts with programs, Cordilleran Section, v. 16, no. 6, p. 689.

Wicks, L., Oliver, B., Heaton, D., Avant, T., Khalighi, A., and Nourse, Jonathan A, 2008, Delineation of the SCE hydroelectric Diversion System and Eroded Segments of the Old Mount Baldy Road in San Antonio Canyon Using GPS / GIS Technology, poster presentation for Southern California Conference on Undergraduate Research, California State Polytechnic University, Pomona.

Woodburne, M. O. 1991. The Cajon Valley. In Inland Southern California: The Last 70 Million Years, ed. M.O. Woodburne, R.E. Reynolds, and D.P. Whistler, 49-51. Redlands: San Bernardino County Museum Association Quarterly 38(3,4).

Woodburne, M. O., and D. J. Golz. 1972. Stratigraphy of the Punchbowl Formation, Cajon Valley, southern California. University of California Publications in Geological Sciences 92, 73 pp.

Woodring, W. P. 1942. Marine Miocene mollusks from Cajon Pass, California. Journal of Paleontology 16 (11):78-83.