Junco hyemalis mearnsi
One of our most common winter birds are the Dark-eyed Juncos. We are fortunate to have
several different varieties. The most common are the Oregon Juncos, followed by the
Pink-sided Juncos, the Gray-headed Juncos, and the eastern-like Slate-colored Juncos.
The problem with Juncos is telling them apart, and that is further complicated by the fact
that many of the races interbreed. There are many good web-based sites that talk about
the Juncos, some very interesting research (especially, see the Indiana University project).

This particular visitor I think is a Pink-sided Junco -- based on the silvery
color of the hood, and the broad pink coloration below the wings.