Abstract The San Gabriel anorthosite-syenite-gabbro body is exposed in the western San Gabriel Mountains about 30 mi (48 km) north of Los Angeles (Fig. 1). The most abundant lithologies of this body, which constitute the anorthosite-leucogabbro unit, are easily accessible via Angeles Forest Highway (N3) along Mill Creek about 18 mi (28.8 km) south of Palmdale (Fig 11, 2A). However, many of the most interesting lithologies of this body can be seen only by driving several mi (km) on U.S. Forest Service roads into he central part of the body west of Angeles Forest Highway. These localities can be reached from Angeles Forest Highway by driving west from Mill Creek Summit, past Mt. Gleason, to North Fork Saddle, and on down Pacoima Canyon. Alternately, they can be reached by driving east either from Santa Clara Divide or from Dillon Divide on the Sand Canyon-Little Tujunga Road (Fig. 1). A second important group of lithologies constitutes the syenite unit and can be seen near “Sold” on the North Fork Saddle-Magic Mountain-Mount Gleason road (Figs. 1, 2B). This road is usually in good condition and is easily passable by conventional automobile except between December and February, when it is occasionally covered by snow at higher elevations. A third important group of lithologies constitutes the Jotunite unit and can be seen along Pacoima Canyon (Fig. 2C). The road through Pacoima Canyon, reached from either Dillon Divide or North Fork Saddle (Fig, 1), is rough and may require use of a four-wheel-drive vehicle during winter and spring.

Abstract The Devil's Punchbowl, now a county park, is a spectacular exposure of Tertiary sandstone strata on the southwest margin of the Mojave Desert adjacent to the San Gabriel Mountains. This unusual feature is located south of Valyermo Ranger Station, about 7 mi (11 km) southeast of Pearblosso in the Mojave Desert in northern Los Angeles County (Fig. 1). It is between the high San Gabriel Mountains to the south, and lower hills to the north, which hide it from the adjacent Mojave Desert. The Devil's Punchbowl is on and within the north border of the Angeles National Forest. This site is accessible via a paved road (L.A. County Road N6) direct from Pearblossom on California 138. The Devil's Punchbowl is shown on the Valyermo 7 1/2- and 15-minute Quadrangles. The geology described here is summarized from Dibblee (1967).

Abstract The spectacular, trench-like roadcut where the Antelope Valley Freeway (California 14) crosses the San Andreas fault zone not only excellently exposes the geology within the zone but is also the most readily accessible point on the San Andreas fault for residents of the Los Angeles region. The locality is 60 mi (100 km) from the Los Angeles Civic Center via I-5 ad California 14, and is about 1 mi (1.6 km) southwest of the city of Palmdale between the offramps for Palmdale Boulevard and Avenue S (Fig. 1). The Antelope Valley Freeway is a limited-access, divided highway; stopping along the shoulder to view the geology is not permitted. Slowing down while traveling through the cut is also very dangerous because of high-speed freeway traffic. The best way to view the roadcut is to exit the freeway at Avenue S and climb the hill outside the fence along the freeway.

Abstract This stop is located in the Pacific Palisades areaof the City of Los Angeles, directly west of the Sunspot Restaurant and Motel, 15145 Pacific Coast Highway, between traffic signals at Chautauqua Boulevard, 0.5 mi, (0.8 km) to the southeast, and Temescal Canyon Road, 0.6 mi (1.0 km) to the northwest (Fig. 1). The mouth of Potrero Canyon is situated behind the motel. The site can be reached from central Los Angeles to the east via the Santa Monica Freeway (I-10), which continues west of the McClure Tunnel in the City of SantaMonica as the Pacific Coast Highway (California 1), or from the Ventura-Oxnard area to the west via the Pacific Coast ing is Highway through Malibu. Parking is available directly west of the restaurant-motel, or, for afee, directly across the highway; during periods of beach use on summer weekends, parking may be difficultand heavy traffic may be a problem. Extreme care should be taken if it is necessary to cross Pacific Coast Highway.

Abstract One of the best exposures of the Sierra Madre thrust fault can be seen in the west wall of Santa Anita Canyon in Wilderness Park, city of Arcadia, 15 mi (25 km) northeast of downtown Los Angeles. Figure 1 shows how one can drive to the fault exposure by turning left into the first available parking area in Wilderness Park. The park gates are open 900 am to 5:00 pm daily. The 54-mi-long (90 km) Sierra Madre fault zone forms the southern base of the San Gabriel Mountains along which they have been thrust over the valleys to the south. The 1971 San Fernando M 6.4 earthquake, caused by this fault, created 15 mi (25 km) of surface ruptures beginning 24 mi (40 km) west of this exposure.At the west side of Arcadia’s Wilderness Park (Fig. 2), banded gneiss is thrust over old alluvium containing large boulders. The fault consists of several feet of gouge and crushed rock generated from the gneiss; it dips 35 degrees north. The fault cannot be traced into the upper part of the old alluvium and probably has been inactive since it was deposited, roughly 2,000 to 5,000 years ago (Crook and others,1978). Two of the earliest geologists to describe the San Gabriel Mountains (Davis, 1927; Miller, 1928) believed the range was bounded on the south by normal faults. Mason Hill (1980) was first to show that the western part of the range was not created by the typical basin and range-type faulting. In the late 1930s, John P. Buwalda (1940) mapped portions of the fault zone between La Canada and Monrovia. He was the first to describe the Sierra Madre fault as “a rather wide zone complexly braided as to pattern of fracture lines” rather than a single line trace. It was not until the 1960s that portions of the fault zone were mapped in detail. This mapping was done bya group of Metropolitan Water District (MWD) of Southern California geologists of which the authors were a part. The 1:12,000 scale mapping was carried out between the ArroyoSeco on the west and Sycamore Canyon on the east andestablished 11 localities where crystalline basementrocks could be seen thrust over Quaternary alluvium. The Wilderness Park site was, to our best recollection, discovered during this project by Daniel C. Kalin and isjudged by us to be the best easily accessible example. The first published map showing the fault zone and the Wilderness Park site was produced by Douglas M. Morton(1973). His map shows this fault trace to branch into the interior of the mountain range rather than follow the southern base as does the main fault zone. From 1975–78 the authors, along with C. R. Allen, B. Kamb, and C. M. Payne mapped the fault zone in greater detail, and trenched the fault, as part of a USGS grant to Caltech (Crook and others, 1978). The area mapped is a strip 1.2 to 2.4 mi (2 to 4km) wide extending 24 mi (40 km) from Big Tujanga to San Gabriel Canyons. The 14C dates obtained from the Caltech work reveal that the central part of the Sierra Madre fault has notmoved in 5,000 years. This contrasts with the 1971 earthquake to the west and the recent evidence that the Cucaonga branch to the east has a recurrence interval of about 800 years (Morton and others, 1982). Is the central part of the fault zone truly orders of magnitude less active, or has it accumulated enough strain energyto be currently worrisome?

Abstract The Ventura basin in the Transverse Ranges of southernCalifornia (Fig. 1) contains evidence for major folding and faultingin Quaternary time, deformation that is still in progress. Muchof the evidence for age and deformation rates comes from theVentura Avenue anticline that began to form about 200 Ka. The locality exposes the axis of the western continuation of this anticlineand a folded reverse fault similar to larger ones known fromsubsurface information.

Abstract Exposures of turbidite features in the Pico Formation arelocated in Santa Paula Creek along the east side of CaliforniaState Highway 150, 3.1 mi (5 km) north of Main Street, SantaPaula (Fig. 1). Santa Paula is 14 mi (22.4 km) east of the city ofVentura, Ventura County, southern California. At the roadside entrance to the site, there is a chain and a not respassing sign. Permission to enter may be obtained from the Santa Paula Water Department (805-525-5591). The best exposures of the strata start at a silted dam and gauging station andcontinue south for about 600 ft (180 m). Santa Paula Creek crosses the steeply dipping strata at a right angle, thus providing an excellent cross section for study (Fig. 2).

Abstract Wheeler Gorge is the narrow part of the North Fork of Matilija Canyon that cuts through the Santa Ynez-Topatopa Range of the western Transverse Ranges, in Ventura County. This canyon is within the Los Padres National Forest.Wheeler Gorge is accessible from California 33 which passes through it and Wheeler Springs, a small resort in this canyon 1 mi (1.6 km) west of Wheeler Gorge. Wheeler Springs is about 19 mi (30 km) north of Ventura on the coast and about 7 mi(11 km) northwest of Ojai in Ojai Valley (Fig.1). At Wheeler Gorge the canyon is so narrow and steep-walled that three short tunnels had to be cut and three bridges built for California 33.The North Fork of Matilija Creek and Wheeler Springs are shown on the Wheeler Springs 7 1/2-minute Topographic Quadrangle of the U.S. Geological Survey.

Abstract The central part of Ridge Basin is easily accessible by automobile or bus from I-5, the eight-lane freeway between Los Angeles and Bakersfield, California (Fig.1). Leave the freeway at Templin Highway and visit the localities in the order of their numbering, if time allows. If time is short, visit in this order: 4,3, and 6. All seven localities can be visited in one full day and only locality 4 (Frenchman Flat) requires walking, and then for only about 0.6 mi (1 km), into the narrow gorge southwestward along Piru Creek. Buses can get to all stops except 1 and 2. All are on public land administered by the U.S. Forest Service, including Oak Flat Campground, which has tables, piped water, and pittoilets. Most of the stops are on the WhitakerPeak 7½-minute Quadrangle.

Abstract From either the coast or the interior, Wallace Creek is most easily reached by way of California 58 (Fig.1). Precisely at the southwestern base of the Temblor Range, leave California 58 and drive southwest onan unmarked paved road about 0.2 mi (0.3 km) to a junction with an unpaved road (Fig.2). Turn left (south) on this road and follow the San Andreas fault to Wallace Creek.The unpaved road leading to Wallace Creekis impassable to all vehicles during and immediately following major storms.At all other times, two-wheel- or four-wheel-drive vehicles can be easily driven to within 1,300 ft (400 m) of the site. To avoid the gradual destruction of fragile tectonic landforms, park vehicles along the road near the section 33/34 boundary fence and walk theshort distance north to the fault. During the dry season, be careful not to park on dry, flammable vegetation.

Abstract Point Lobos, a prominent headland at the southern side of Carmel Bay on the central California coast (Fig.1), is the site of a popular state reserve. Entrance to this reserve is from California 1, about 4 mi(6.4 km) south of the village of Carmel and 2.5 mi(4 km) southwest of the intersection of California 1 and Carmel Valley Road (County Road G16). Within the reserve, paved roads and well-maintained foot trails provide excellent access to many of the more prominent exposures (Fig.1). Outcrops not served by foot trails are off-limits to the public; however, the geologically important exposuresdescribed herein are readily accessible. Point LobosState Reserve is beautifully maintained in a pristine condition by its staff, and the rules are strictly enforced. Most important, froma geologic standpoint, are strictures against collecting or disturbing any natural object within the reserve, so geological hammers are best left in vehicles. The rocks of the reserve are a striking esthetic resource and a mecca for amateur and professional photographers—they are not to be defaced. The reserve opens in the morning (typically at 9:00) and closes before sundown. A nominal entrance fee is charged to visitors.

Abstract The Pacheco Pass-San Luis Reservoir area is located in the central Diablo Range along the crest and eastern flank of the uplift. The site is transected by California State Highway 152, a four-lane, divided roadway near and east of the summit (elevation 1,368 ft; 410 m). The area is situated about 120 mi (200 km) southeast of San Francisco and 285 mi (450 km) northwest of Los Angeles. The location is illustrated in Figure 1. Access is provided by Highway 152, and a portion of the former road; four of the six outcrops referred to in this report are roadcuts. Because of heavy automobile and truck traffic on Highway 152, special care must be exercised when examining the rocks, and vehicles should be parked in turnouts or on the shoulder well off the pavement.

Abstract This site is located adjacent to the California coast in northern San Mateo County, about 15 mi (25 km) south-southwest of downtown San Francisco (Fig. 1). From San Francisco, take 1–280 south to its intersection with California 1, then follow California 1 southward for approximately 9 mi (15 km) to San Pedro Avenue in Pacifica. From the central San Francisco Peninsula, take California 92 westward to its intersection with California 1 in Half Moon Bay, then proceed northward on California 1 for approximately 10 mi (16 km) to San Pedro Avenue in Pacifica. From the southern San Francisco Peninsula or Santa Cruz County, take California 1 north to San Pedro Avenue in Pacifica. The Shelter Cove locality (Stop 1) can be reached by taking San Pedro Avenue west for three blocks from California 1, turning north on Danmann Road, and proceeding two blocks north to Shelter Cove Road. At present (July 1986), Shelter Cove Road is a privately maintained access that has sustained substantial landslide damage and is passable only on foot. The property at Shelter Cove is private, and permission to enter must be obtained from the owners (Telegan Realty, Pacifica, California). Roadcuts along California 1 are located south of San Pedro Avenue. Stop 2 is located 0.7 mi (1.1 km) to the south on the northwest side of the highway. Stop 3 in the Devil’s Slide area is located 0.6 mi (1 km) farther south along California 1 and Stop 4 another 0.7 mi (1.1 km) to the south. Stops 2,3, and 4 are subject to heavy traffic and have limited parking along a narrow, twisting, and dangerous roadway. Exposures are close to the roadway, so great caution should be exercised.

Abstract The Merced Formation and consanguineous superjacent strata are well exposed in seacliffs that extend 4.3 mi (7 km) south from Lake Merced to the trace of the San Andreas fault (Fig. 1). The exposures can be reached by walking south along the beach from oceanfront public parking areas west of Lake Merced or via several well-defined trails that lead to the beach from Fort Funston (Fig. 1), a part of the Golden Gate Recreational Area, which provides public parking. The southern part of the exposure can be reached by walking north from a public parking area at Mussel Rock (Fig.1), which can be reached via an access road from Westline Drive in northern Pacifica (Edgemar). The central part of the exposure is presently accessible via a road to the former Thornton Beach State Park at the western end of Alemany Boulevard. This road, however, is now badly disrupted by landslides and affords uncertain future accessibility. The character of the exposure changes as a consequence of local landsliding and seasonal variation in the level of beach sand. The deposits are best viewed following winter storms when the erosion of beach sand provides for fresh, wave-washed exposure. The observer of these deposits should continually be alert forrock falls and the possibility of being isolated by arising tide.

Abstract The Marin Headlands are the hills on the north shore of the Golden Gate opposite San Francisco (Figs. 1,2; see Point Bonita and San Francisco North 7DDD÷-minute Quadrangles). They are entirely within the Golden Gate National Recreation Area(GGNRA), a unit of the National Park System. Collecting of rock specimens is by permit only, obtainable on adequate scientific or educationaljustification from the GGNRA headquarters at Fort Mason, San Francisco 94123 (415-556-0560). Application for permit should be made at least two weeks in advance of the visit. San Francisco MUNI bus No. 76 runs on Sundays and holidays only, between San Francisco and Fort Cronkhite Visitor Center (FCVC, Fig. 1). For schedule and stops in San Francisco call the MUNI system (415-673-MUNI). The Golden Gate Transit District bus No. 10 makes daily stops at the Alexander Avenue off-ramp (Locality 1, Fig. 1); buses Nos. 20,50, and 80 make daily stops at Spencer Avenue (Locality 2, Fig. 1); and bus No. 10 also stops at Tamalpais Valley Junction, from which a road and trail go to the Tennessee Valley trailhead (Locality 3, Fig. 1). Call 415-332-6600 for the Golden Gate Transit schedule and stops in San Francisco. Automobile access from San Francisco is via U.S. 101 north across the Golden Gate Bridge and the secondoff-ramp (Alexander Avenue) on the north side of the bridge; turn left at first opportunity (about 100 m), go back underneath the freeway, and keep to right up the hill into the Golden Gate National Recreation Area (GGNRA) and Marin Headlands. Approaching from the north on U.S. 101, take the third Sausalito off-ramp (the only off-ramp between the Waldo Tunnel and the Golden Gate Bridge), turn left immediately at the stop sign, and then turn right immediately up the hill at the sign to the GGNRA. The Tennessee Valley Trailhead(Locality 3, Fig. 1) is accessible from California 1 between U.S. 101 and Tamalpais Valley Junction. All travel away from roads must be made on foot, horseback, or bicycle; motorized vehicles are prohibited off designated roads.