Way far west of Island in the Sky, Horseshoe Canyon shelters one of the most impressive collections of millennia-old rock art in the Southwest. The centerpiece is the Great Gallery and its haunting Barrier Canyon–style pictographs from between 2000 BC and AD 500. The heroic, bigger-than-life-size figures are magnificent. Artifacts recovered here date back as far as 9000 BC.
That said, it's not easy to get to. The gallery lies at the end of a 6.5-mile round-trip hiking trail descending 750ft from a dirt road. Plan on six hours. Rangers lead hikes here on Saturday and Sunday from April through October; contact the Hans Flat Ranger Station for times. You can camp on Bureau of Land Management (BLM) land at the trailhead, though it's really a parking lot. There is a single vault toilet, but no water.
From Moab the trip is about 120 miles (2¾ hours). Take Hwy 191 north to I-70 west, then Hwy 24 south. About 25 miles south of I-70, past the turnoff for Goblin Valley State Park, turn east and follow the gravel road 30 miles. From Hanksville it's 45 miles (1½ hours).
