This is an uncommon winter visitor and migrant in California. It first showed up in our yard 9 January shortly after a storm. It has been quite skittish and I was not able to get photos until today. This individual is probably a white-striped morph. This species does not cleanly separate into tan and white striped morphs in the winter. The strong bimodal plumage pattern is normally expressed only in the breeding season. In the winter there is more of a continuum of variation, possibly to facilitate flock cohesiveness (Atkinson & Ralph 1980). However this bird already has more white in its supercilium and less ventral streaking than seen on most adult tan striped morphs.. I believe it will lose the slight tan tinge by Spring. The species is famous for negative assortative mating between the two color morphs. White-striped morphs prefer to mate with tan-striped morphs and vice versa. Nikon CoolPix P510.
Reference:
Atkinson, C.T. & Ralph, C.J. (1980). Acquisition of plumage polymorphism in White-throated Sparrows. The Auk. 97: 245-252. [PDF]