A mountain bluebird to me is the Sierra blue sky come to life, a burst of the vibrant blue dashing over the landscape, as if the sky decided to briefly visit the land to check things out.
Although I am a terrible birder, this is one avian species I feel confident in identifying, for as Joseph Grinnell wrote in his Animal Life in the Yosemite, "There need be no difficulty in recognizing the Mountain Bluebird in its summer haunts, as there is no other bird of similar size with conspicuously blue coloration in the high mountains or on the east slope."
Usually these shy birds make for a tough photo as they typically flutter away when I encounter them, but today this friendly bluebird followed me for part of my hike along the Kuna Crest and curiously checked me out.