Valley of Fire State Park, near the northern tip of Lake Mead, is home to some spectacular scenery where a range of iron-rich red mountains peek out of normally drab valleys. It also contains very well-preserved Indian petroglyphs in many easily accesible locations. It is Nevada's oldest state park and an easy day-trip from Las Vegas.
The trail to 'Mouse's Tank' is disappointing except for a small number of petroglyphs. A better bet is to spend that time touring the rest of the park by car. The visitor's center is a welcome sight so far from civilization and gives a nice geologic and archeologic history of the park. If you are arriving via I-15, stop at the convenience store in Moapa for an interesting (if less than genuine) Indian experience and a Gatorade.