I haven't seen any in the "normal" shooting areas. We like to go rockhounding after shooting, and that's when we see them. Here's a link to the area we like to go. Also, if you follow the creek on the left to where the dirt road heads back west, there is a sandstone formation that sports about 10 of the buggers. Just gotta get out there early enough. They love the morning sun, ya know.
And the east side is private, I think. It's fenced at any rate.
Anyways, here's the link. I hope it works.
http://maps.google.com/maps?hl=en&ie=UTF8&t=h&ll=40.681419,-104.479122&spn=0.057929,0.11055&z=13