City of Rocks National Reserve

The Twin Sisters are not twins. The two granite spires rise about 750 feet above the basin floor at the south end of the reserve, matched in size and shape, but the darker one is roughly 2.5 billion years old, some of the oldest rock exposed in the western United States. The paler one belongs to the Almo pluton, which cooled underground about 28 million years ago. Most of the fins and domes around you are the younger rock, eroded out once a cap of harder quartzite above it wore away.

The emigrants steered by them. Close to a quarter of a million people came through this basin between 1843 and 1882, on the California Trail and later on the freight and stage road from Kelton, Utah, to Boise. Addison Pratt, a Mormon Battalion officer on his way home from California, named the Sisters on September 15, 1848, and the Battalion men opened a road that year from Granite Pass to Salt Lake. It met the California Trail about a mile and a half south of the spires, and from the junction one road went on over the pass. When the trails opened, Granite Pass lay in Mexico, less than a mile from Oregon Territory. The springs and grass along Circle Creek, where many of them camped, were Newe country long before the wagons.

Today more than half of the reserve's hundred thousand yearly visitors come to climb, on granite that draws people from around the world. Castle Rocks State Park next door shares a visitor center in Almo. Gravel roads loop through the spires, and some close in winter.