This species is much less common than the Greater Yellowlegs in California and is usually encountered only as a migrant rarely remaining during the winter. This is a juvenile, hatched this year. It has only one generation of feathers, all fresh and new.
The two species of yellowlegs can be difficult to tell apart. David Sibley has a helpful recent essay on the subject in his blog.
Digiscoped with Panasonic DMC-LX5 | Nikon FieldScope III | 30XWA | hand-held (no adapter).