This is an abundant wintering bird in the lowlands of California, but breeds in the mountains and to the North. This is the typical Western form D. c. auduboni formerly known as "Audubon's Warbler" which has a yellow throat. This uncropped photo shows the difference between the rump and the uppertail coverts. It is the rump which is yellow and the uppertail coverts are the two rows of gray feathers with broad black shaft streaks, between the rump and the tail. These terms are frequently confused in descriptions.
Olympus D-550z / Nikon FieldScope 3 / 30XWA (hand-held - no adapter).