Brewer's Sparrow (Spizella breweri), photographed on Bodega Head on 2 September 2017.
I don't have much experience with this species, but I could tell it was different right away. Compared with the resident White-crowned Sparrows, it was much smaller and paler. Note the relatively subdued facial markings and the prominent white eye ring.
Brewer's Sparrow is a rare fall migrant in this area. This is the first time I've seen one on Bodega Head. I saw it briefly, snapped a few quick photos, and then it flew off to the east and I could not relocate it.
From the Birds of North America —
"Most individuals breed in and around Great Basin and winter in Sonoran and Chihuahuan deserts of sw. U.S., w. Mexico (including Baja California peninsula), and Mexican Plateau."