American Pipit, Anthus rubescens
They winter on short grass and stubble fields, plowed fields, the edges of marshes, and beaches, usually in small flocks, around the Bay Area.
This pipit, wintering in the Central Valley of California, has a less contrasty head, and less extensive streaking on the underparts, than the other pipits shown on this page; I'm curious if this suggests a different age (first-cycle) or a different subspecies, or is consistent with normal individual variation.
American Pipits live mostly on insects, like this earwig, though on their wintering grounds they also eat seeds.
Here's a wintering pipit on the beach.
And here's one, above, on the frozen fringe of a Central Valley pond on a cold winter morning; below is the same bird seen face on.
The plumage is pretty effective camouflage in the short dry grass where many of these birds spend most of their winters.