It’s all over the Matt Davis trail.
I think I’ve figured out that the mystery call I’ve been wondering about, 2 or 3 starting notes accelerating into a trill, is a Wrentit. The recording sounds right, and the natural history of the Point Reyes Peninsula in the Stinson Beach house describes this sort of terrain as permeated with the calls of White-crowned Sparrows and Wrentits. The White-crowned Sparrows produce the rising wheezy trill-buzz.
Today I saw what I think was a Pine Siskin: yellow wing edges and rump, white wingbars, a pointy sparrow-like beak, and a beady black eye.