While the west has never had anything close to the number of secondaries as the east or midwest, I can think of a few on the west coast. Most of these did not start life as a secondary, but over time became one... Most of these that are still around had a decent bit of local traffic, though not all.

1.) SP's West Valley Line - (Davis, CA to Tehama, CA). At one point was a used for bay area to PNW traffic, while most of the traffic was on the East Valley Line (Roseville to Tehama). Was leased off to the Cal Northern in the early 90's. Currently all in service except the northern most few miles between Tehama and Richfield.

2.) SP's West Side Line - (Tracy, CA to Fresno, CA). Hosted at least a few passenger trains and freights. Again most action was on the mainline to the east. Middle section torn out, southern section leased/sold to the San Joaquine Valley RR, northern section leased/sold to the Cal Northern.

3.) SP's Siskiyou Line (Black Butte,CA to Springfield Jct., OR). SP's original line north to Oregon. The Natron cutoff replaced it as the main line with far better grades and curves, and a shorter distance to boot. SP kept it for the online lumber traffic, running a handful of trains on it. It was sold (north of ~Ashland, OR) and leased (south of ~Ashland) to Central Oregon and Pacific in the early 90's. Whole line is currently open, and trains traverse the entirety of it, though treated more like a branch than anything else. UP did detour a train or two over this line a few years back there was an issue with a Tunnel on the Cascade Line (Natron Cutoff).

4.) SP's Coast Line (San Jose,CA to Burbank, CA). Built as a direct route from the Bay Area to the LA Area, it always was more of a passenger route than a freight route (though has seen plenty of freight at times). With the demise of SP passenger trains, and moving freight classification in the LA basin from Taylor to West Colton it became a secondary. UP ran some decent traffic on it early on, but the last 10 years have seen very little through traffic, and at this point it's all just locals and Amtrak.

5.) SP Saugus Line (Palmdale, CA to Burbank, CA). SP's original line from the Mojave Desert (east end of Tehachapi Pass) to the LA area. Was mostly obsoleted with the opening of the Palmdale Cutoff and West Colton Yard, though a small amount of freight traffic remained. Metrolink now owns it, and runs their commuter trains on it. UP still runs a handful of trackage rights trains.

6.) Much of the ex-WP (Weso, NV to Stockton, CA ...at minimum). UP only runs a few trains a day over this portion of the ex-WP. Mostly slow heavy westbounds that can take advantage of the lower grades, and are not going to be hurt by the much longer route (as compared to Donner Pass). Between Keddie and Stockton BNSF uses trackage rights for their Inside Gateway trains, but once you are east of Keddie it can be a pretty lonely railroad.

7.) NP's Stampede Pass Line (Aubern, WA to Pasco, WA) NP's original mainline to the Seattle/Tacoma Area. With the BN merger, this lines importance dropped as the ex-GN Stevens Pass and ex-SP&S Columbia River Gorge lines parallel it. Parts of it were lease to shortlines, and other parts mothballed, but BNSF brought it back to life in the late 90's to add capacity. It is currently used predominately as an alternate routeing for empty eastbound unit trains.

Well there are a few anyways... Lets see what others come up with.

Best regards,
~Matt