Answer:

The habitat in which this bird was seen allows us to narrow it down quite a bit. Though its appearance is superficially thrush-like, neither Hermit nor Swainson’s Thrushes are found in such open, arid habitat. Sparrows, Thrashers, Horned Lark, or American Pipit are among the only possibilities.

The bird is too large to be a sparrow, and though its legs are partly hidden, we can see that they are rather longer relative to body size than most sparrows’ legs. One foot is raised while the other is on the ground: the bird is clearly walking. Many species of sparrows would be more likely found hopping.

The bird is quite clearly not a Horned Lark, lacking the dark breastband, mask, and “horns” that make the Horned Lark so distinctive. It was also solitary, while Horned Larks tend to flock together. In fact, just across the two-lane highway from where this bird was seen, there was a flock of Horned Larks, with which this bird did not associate at all. The Larks also regularly took flight briefly, while this one remained on the ground, running rather than flying from place to place.

With its dark auriculars outlined in lighter gray-brown, streaked breast, and whitish wingbars, the bird may resemble a pipit. However, it is stockier than a pipit, pipits typically only winter in this area and would be gone by late March, and like Horned Larks, pipits are typically found in flocks.

That leaves the thrashers. The bird’s bill is not strongly decurved, ruling out California, Crissal, and LeConte’s. Of the relatively straight-billed thrashers, Brown and Bendire’s are highly unlikely given their ranges and where this bird was seen, leaving only the Sage Thrasher.

The bird’s field marks–whitish wingbars, brown auriculars, crisp streaking on the underside and sides, and the faintly visible pale iris and white tail corners–also strongly support the conclusion that this is a Sage Thrasher.

Congratulations to Henry W. and Adrian for figuring out Sage Thrasher! This one was quite difficult.