This little guy is a Brewer's sparrow. In some places they're abundant. In this nice fresh plumage they're very gray overall, much more so than I remembered the couple of late summer birds I'd encountered in the past
Vesper sparrows are present in smaller numbers. One was singing a continuous dry warbling song, very different from their phrased whistled song on breeding territories. Apparently some of the birds have different winter songs according to Stuart.
White-crowned sparrows are abundant, the males are already in full breeding plumage (obviously this is not an adult male):
I've always associated Lincoln's sparrow with moist places so was quite surprised to see one. I've since seen several though. They seemed shier than when up north.
Here's the local song sparrow. It's much whiter in ground color than ours. The brown is also much more rufous (which doesn't show up very well on my monitor with this pic).