Here are two groups of three pictures each, taken a little more than a minute apart at Wheeler Sheep Camp, Kyburz Flat, Sierra County, on June 4, 2014, showing an Empidonax flycatcher. I didn't hear the bird vocalize or see identifying behavior. My best guess is that it is a Gray Flycatcher; note the complete lack of color on the underparts, and (shown in one picture) an apparent black tip to the orange lower mandible.