Tent Rocks is only an hour away, so why aren't you already there, looking at 7 million-year-old cones and hunting for obsidian? (Note: You're not actually supposed to take the obsidian, but there's no crime in looking for it.) Open from 7 a.m.-7 p.m. in the summer. 761-8700.
http://www.blm.gov. $5.