Black-chinned Sparrow. Warner Springs, California. April 13, 2014. Greg Gillson.
I found Black-chinned Sparrows! This is one of 5 target birds I was wanting to find this spring. It is found in higher elevation dense chaparral. It's a small gray sparrow, looking quite a bit like a Gray-headed Junco.
I specifically searched near Warner Springs, where these birds have been reported in the past on eBird.