In the Marble Mtns of the East Mojave the most common specimens are trilobites (Ollenelus) from the Lower Cambrian Latham Shale. While cephalons and spines are common, whole specimens are rare. There is also marble and dolomite nearby. The directions from Barstow are: take I-40 west out of Needles and get off on the Old Historic Highway 66 and proceed to the intersection with Cadiz Rd. a few miles east of Amboy. If you are planning to spend the night, bring water, food and camping equiptment.
Coalinga, arroyos and washes immediately south of town are a reasonable source of fossils. Be careful of private property in the area. There's a nice mining and historical museum in the town that's well worth visiting too, including a good minerals display. (Coalinga is located in central CA, along Interstate 5.)
At Los Olivos, north of Santa Barbara, there are lots of road cuts with NICE collecting; mostly jasper/nephrite combinations but some fossils, you need to go into the hills above the town to get to these road cuts.
East of Carpinteria, between US 101 and Route 150 on Bates Road, gastropods are found in the Pleistocene sandy muds.
Bluffs west of Isla Vista contain late Pleistocene mollusks. The bluff is a wave cut terrace from the Pleistocene and contains lots of shells, most of species still which are alive. A ladder is useful.
Capitola, near Santa Cruz, on the beach is a good site for Pliocene fossil collecting. Clams, snails and sand dollars. They are in the sandstone of the sea cliffs and in the talus that falls on to the beach. Go at low tide, walk a few hundred yards south of the Esplanade at Capitola past the sewage outfall.
Topanga Canyon, near Los Angeles, contains middle Miocene sandstone and siltstone from the Topanga Canyon Formation, Cold Creek Member. Abundant gastropods and pelecypods -- mostly replaced -- are found, especially best after a rain when the fossils are often washed out of the matrix. Directions: from the Ventura Freeway (in the San Fernando Valley), get off at the Valley Circle/Mulholland Drive exit Turn left onto Valley Circle, cross over the freeway and proceed onto Mulholland Drive. Turn right onto Valmar Avenue -- Valmar becomes Old Topanga Canyon Road. At Mulholland Highway, bear right and prepare to turn left back onto Old Topanga Canyon Road in 1/8 mile. Turn left and proceed up Old Topanga almost a mile, past the point where the road switches back upon itself. From this point until the top of the hill, you will encounter fossiliferous road cuts on your right. The first embankment contains a massive oyster reef.
The San Pedro area has several Pleistocene marine outcrops. The most accessible (and prolific) is the freeway embankment above John Gibson Boulevard. These are from the middle Pleistocene San Pedro Sand at the bottom of the bank and the late Pleistocene (~120,00 years bp) Palos Verdes Sand at the top. Directions: from LA proceed south on the Harbor Freeway (110) towards San Pedro, get off at the C Street exit, turn right at the first stop sign (Figueroa) and, one block further, right again onto John Gibson Blvd. Drive 1/2 mile and park. Climb up the embankment and dig at the levels that show signs of previous fossil collectors' activity.
Rincon Point near the Ventura/Santa Barbara area, contains Plio/Pleistocene marine fauna. This locality is a freeway cut that exposes sixteen different strata of the Santa Barbara Formation -- each with its own unique makeup and fauna. Directions: from LA, travel north on the Ventura Freeway (101) towards Ventura. Travel about an hour, north towards Santa Barbara. Exit onto Highway 150 (towards Lake Casitas) and park immediately after leaving Route 101. The fossils are found along the freeway offramp and up the hill above.
Coal Point, Isla Vista, a little bit north of Santa Barbara, is a beach locality is from an unnamed late Pleistocene formation. Directions: Drive north on the 101 Freeway through Santa Barbara and Goleta. Take the Storke Road (Glenn Annie Road) exit and turn left. Turn left onto El Colegio Road, right on Camino Corto and right again on Del Playa Drive. Park and walk down to the beach. The fossiliferous layer is visible in the beach cliff and, as you walk north, becomes more accessible and prolific. NOTE: keep an eye out for black widow spiders.
Crown Point, near San Diego has an unusual outcrop of the late Pleistocene Bay Point Formation, with large echinoids. Directions: Take the Grand Avenue exit off of the 5 freeway south -- towards Pacific Beach. Take Grand to Ingraham Street, make a left, then turn on La Cima Drive. Park at end of La Cima (at Riviera Drive) and walk down the stairs to the beach. The echinoids are found in a donax coquina/sandstone south of the stairs to the tip of the point.
Point Loma, near San Diego is also from the Bay Point Formation, and contains an interesting tide pool fauna and great scenery. Mostly mollusks are found, representing an interesting collection of tide pool residents -- many different limpets and the occasional abalone. Directions: From the 5 freeway south towards San Diego, get off at the Tecolate Road/Sea World exit. Proceed west on Sea World Drive -- past Sea World, it becomes Sunset Cliffs Blvd. Drive to the end of Sunset Cliffs and park in the lot for Sunset Cliffs Park. Look along the top of the sea cliff.
At Jack's Peak near Monterey, there are fossils of little leaves and shells in shale a hundred yards down the trail from the west parking lot. Also, there's lots of jasper at Point Lobos, 5 miles south of Monterey.
Near Cadiz - From Barstow head east on I-40 for about 30 miles or so to Ludlow, then take old Route 66 to Amboy. Take the old highway east for about 15 miles or so. You'll come to a small out of the way place called Cadiz. From there head south on a chip sealed road till you get to a military(?) installation of some sort. There are also train tracks with very frequent trains rolling by. The road veers to the left and becomes a "washboard" dirt road. It paralells the RR tracks. Take that about 1-2 miles and keep looking towards the north. The Marble Mts (really part of the Old Woman Mts) are in that direction. There are roads heading north from the dirt road that lead to what appears as a greyish outcrop of limestone set amongst brown rocks. That is the Chambliss (Cambrian) limestone. Stratigraphically beneath the limestone is the Cadiz shale home of the Olenellus trilobites. In the nearby lower beds of the quartzite are found the banded agates that range in size from a marble to a grapefruit. The key to finding this area is to pick out the limestone outcrop. It is about two miles from the dirt road that paralells the RR tracks.