We spent the night in Twentynine Palms, just north of Joshua Tree Nat. Park and planned a desert backroad route up toward Death Valley. About 50mi. north of Twentynine Palms I had noticed a big black smudge on Google Earth: a lava flow with a hiking destination called Amboy Crater. http://www.blm.gov/ca/st/en/fo/needles/amboy.html
This turned out to be a pleasant walk, reminiscent of SP Crater above Flagstaff though less high and steep. There is a nice facility and trail maintained by BLM and its well worth a stop. The sound of explosions and machine gun fire from "nearby" Marine training adds to the excitement.