City of Rocks National Reserve
and State Park, Idaho

The City of Rocks National Reserve, as a 14,407-acre property (mind you, about 1/4 of it is privately owned), was first designated by Congress in 1988 and is cooperatively managed by the Idaho Department of Parks and Recreation and the National Park Service. The area was given the name "City of Rocks" by travelers on the California Trail in the early 1840's. This cluster of upthrust granite rocks was a landmark on the northern edge of the Great Basin Desert for emigrants on the California Trail (1843), Applegate (Oregon) Trail (1846) and the Salt Lake Alternate Trail (1848). Some of these emigrants were among the first graffiti artists in America, writing their names on the rock faces with axle grease (that still shows today).

Located as it is in southern Idaho against the northern edge of the Great Basin in the Albion Mountain Range, the climate is reasonably pleasant from April through October, although summer days can see lows in the 30's and high's near 100°. Because of the elevation, you're also going to want some good sunscreen.

Recreational activities at the City of Rocks include hiking, backpacking, rock climbing, picnicking, horseback riding, Nordic skiing, wildlife viewing, photography, and primitive camping in designated areas. The visitor center is in Almo and is open Monday through Friday 8:00 AM to 4:30 PM. The road through Almo is open year round but the City of Rocks Backcountry Byway may be impassable in winter.

The granite in the park can be of radically different ages. An example is the Twin Sisters formation. In the photo below, the Sister on the left is 2.5 billion years old and part of the Green River Complex. The Sister on the right was formed about 25 million years ago and is part of the Almo Pluton. The Almo Pluton was hot magma that forced its way up through the much older Green River Complex and then solidified. At the time this was happening, both layers were still far underground. Over time, the overlying rock has eroded away and the formations beneath have risen and cracked. Erosion then works faster in the cracks and fissures, creating what we see today.

Another element of erosion is "frost wedging:" water seeps into cracks and fissures and expands when it freezes. This action can cause large rock slabs to break off the original formation. This process has already removed some of the layers of rock scarred by those graffiti artists only 160 years ago.

So then, all this erosive "sculpting" has created pinnacles and spires reaching as much as 600 feet above ground. More than 700 climbing routes have been developed at the City of Rocks, most of these on rocks between 100 and 300 feet high. The visitor center offers quite a few privately published climbing guides for sale. While you're in there, you can also get up-to-date information on conditions and area restrictions.