While birding in Boot Canyon, Big Bend National Park on 4 September 2004, I ran across what I quickly determined to be an adult male Hermit Warbler.   Returning home and inspecting a few (rather fuzzy) photos I took of the bird, I decided that what I may have had instead was a Townsend's x Hermit Warbler (a hybrid of the 2 species).   What I didn't pick up during my observation was the rather olive-green back and yellow wash on the upper breast.   Some of the pictures hint at a dark cheek patch which I'm rather sure wasn't present and are likely just an effect of shadowing - the middle-left photo shows the bird as I recall it, with a rather clear yellow face (with full yellow eye-ring).