Had to go back and key this one out, after getting it wrong the first time. The very contrasting facial pattern seems to make this a bird a better candidate for Clay-colored, rather than Brewer's. (I've also seen Clay-colored at this spot before, while Brewer's is much rarer in the county. )

I also now think this was the same bird seen twice in two nearby spots, once while heading out and then again while coming back from my walk. (Thank you, @a-tristis, for catching my error the first time.)