I was out hiking with my dog and saw about 5 of these Abert's squirrels, the most I've ever seen. I can't take pictures due to not having any telephoto lens. But they were the dark grey variety. I think quite pretty creatures with the shiny grey-black coats, grey and white tails and black tufted ears. I think they only eat parts of Ponderosa pines and do not store food. Included a weblink for them, has a few nice pix:
http://www.mammalogy.org/aberts-squirrel