Red Rock Canyon National Conservation Area.
The park is this pretty vast area of red and brown mountain outcroppings rising up from the desert floor, and a world set completely apart from the flash and cheese of Vegas. Yesterday, I ran the White-Loop/La Madre Spring loop, a little over 6 miles, with not much more than a 1,000 feet of elevation gain. The loop took me on a crushed gravel trail around the backside of a large sandstone outcropping into the LaMadre wilderness area before circling back up over a pass that afforded great views of the desert valley. I went through pinyon pines, lots of scrub brush, and ran pass old Navajo agave roasting pits and hand prints on rock walls (OK, the hand prints were near the parking area and carefully roped off -- I didn't just stumble on those). Although I missed any wildlife sightings -- save a few lizards -- the area is a known hangout for all sorts of desert and mountain animals, from bighorn sheep and mountain lions to scorpions and gila monsters. Oh, there are also wild burros and horses in the area. The weather was gorgeous, dry with temps climbing from the high 40s into the low 70s while I was there (typical winter weather!).
In short, it was an all-around great experience, something I would recommend for anybody that ends up being in Vegas for some reason!