I don't think they are actively producing oil in Colorado any more. (Natural gas, yes, from coalbed methane, both down around Durango and up near Rifle. I don't think the Denver basin is actively producing any more, though. I could be wrong, though... I'm not in the industry.)
I think they're producing in western Wyoming again, though. (They found that oil late in the boom, I think.) And there's a new find in eastern Utah, too. They're refining the oil in Salt Lake City, I think. At least, that's the reason I've heard for the lower gasoline prices up there.