What Is It?

Granite Rock rises out of the ground in southern Idaho, weathered over the years to create fascinating geologic formations. Sitting in Almo, City of Rocks National Reserve was formed in 1988. It contains more than 14,000 acres and rocks hundreds of feet high.


Much of City of Rocks’ namesake geologic formations are granite base-ment stone—rock that is part of the Earth’s crust, typically far beneath the surface—that juts out. The Green Creek Complex features stone that is 2.5 billion years old, making it some of the oldest rock in the United States.


The Widow Arch Trail is a good place to start, with a 250-foot trail to a stone arch that spans more than 20 feet. A second option is the 1-mile Geological Interpretive Trail, with interpretive stations teaching the differences among the various rock formations.

A Winter Trek

During winter, the reserve is typically covered by blankets of snow, turning it into a great site for snowshoeing or cross-country skiing. Although trails are not groomed, snow-shoeing and skiing are allowed.  Unplowed camping road loops provide flatter paths.

More Information

It costs $7 for a vehicle to enter City of Rocks National Reserve. To start planning your trip and for updated information, visit www.nps.gov/ciro or call 208-824-5901.