As you enter the Swell from the northwest, you follow geologic history back in time. From youngest on the top to oldest on the bottom, the strata include mostly sandstones of the Carmel Formation, Navajo Sandstone, Kayenta Formation, Wingate Sandstone, Chinle Formation, and Moenkopi Formation, which were formed in a variety of depositional environments (rivers, deserts, and shallow seas).

The Swell is an uplifted area where sedimentary rock layers were pushed upward into a dome-like mountain formation called an anticline. Forces in the Earth’s crust created this formation about 40–70 million years ago.

Millions of years after the anticline was formed, erosion wore away at the Swell’s crest, exposing millions of years of natural history. The oldest rocks (around 300 million years old) are near the center of the Swell, surrounded by a ring of younger rocks (100 to 230 million years old).

Outlaws, like Butch Cassidy once hid from lawmen in these cracks, caves, and canyons. In the late 1800s the “Dirty Dozen” and Cassidy’s “Wild Bunch” made their homes in the plateaus of southeastern Utah and along the famous Green River. In fact, one of the boldest robberies in US history was pulled off in Castle Country.