Where to Catch Out in California

Dunsmuir
Crewchange in Dunsmuir is generally fairly fast, unless no crews are available. If you pull into the lower yard and stop, you're going to be around for awhile. If you pull straight through to the depot, you'll change crews and be on your way.
Oakland
Oakland is hard to catch out of heading South. SP and UP both have yards there. Trains come out pretty fast. Bulls are around often.
Portola
Portola is a small town on the UP mainline in the Sierras. It is the normal crew change point after Stockton. There is a small yard, and it is very easy to catch trains here, and plenty of traffic.
Roseville
Roseville is another ideal out spot. All westbound SP over the northern route heads to Roseville, best for catching to Oregon and Seattle. Small bull activity, enormous yard that is worth presurveying on maps. Switchmen range from "Don't know nothin'" to "hold on, I'll call the tower and find out what track they're making up the train of Oakland on." If heading north, you can hang around the curve where the train turns north out of Roseville. The trains creep by until the rear car clears the turn and then picks uRoseville's POs (Police Officers) can be very active at times - I've had friends who were dogged by them all day, they KNOW what you're doing there!
Stockton
Stockton has three yards (SP, UP, and ATSF). The SP and UP yards are pretty easy to catch out of. Trains leave the yard pretty slowly. UP stack trains heading South go to Oakland. UP trains heading North mostly go to Omaha.
Warm Springs
Warm Springs is a small SP hump yard near Milpitas in the Bay Area. It is fairly active, but mostly handles local traffic. Sometimes, SP trains heading South out of Oakland will stop here to pick things up. Warm Springs also serves local trains to/from San Francisco.