The gray flanks and underparts, the relatively thin bill and long primary projection identify this bird as a MOUNTAIN BLUEBIRD. A female Western Bluebird would have warmer tones to the breast and flanks, a shorter bill, steeper forehead, and shorter primaries. Western Bluebirds typically have less white in their tertial edges as well as less white on their wing covert tips and edges (although the covert edges are not strongly marked in this bird).

This Mountain Bluebird was one of two found in Panoche Valley and is an earlier arrival than I would typically expect.