Dave, I have heard very good things about boondocking and mountain biking in the Manti La Sal mountains, near the Four Corners area:
Manti La Sal bikingAlso, speaking of May in the high desert, have you ever camped out on the Rainbow Rim in the Kaibab Nat Forest on the North Rim of the Grand Canyon? We were there in late May, several years ago -- very cool and green, with a fantastic trail right on the edge of the canyon. We are (at best) intermediate non-technical riders and had no trouble with the trail -- several days of great riding and world-class camping.
