SURVEY NOTES

GeoSights: Slot Canyons of the San Rafael Swell, Emery County

Magnificent badlands of colorful and highly eroded sandstones

by Torri Duncan


Aerial view west of the San Rafael Reef at the south end of the Swell with labels for the geologic units by layer and rock color.

Aerial view west of the San Rafael Reef at the south end of the Swell.

Did you know Utah has one of the highest concentrations of slot canyons on Earth? There are well over one thousand slot canyons in the southern part of the state. Slot canyons are long, narrow channels with steep rock walls typically eroded into sandstone or other sedimentary rocks over millions of years. Most slot canyon walls are at least 10 times as high as the width—think of dropping a coin into a coin slot. These narrow geologic features can offer a colorful display of geology, adventurous hikes and rappels, and unique potential hazards.

Some of Utah’s best slot canyons are in the San Rafael Swell (the Swell) where at least forty slot canyons have been explored. They range in difficulty from roadside strolling to technical rappels and canyoneering. U.S. Interstate 70 runs through the center of the Swell and has many scenic viewpoint pullouts to marvel at the meandering slots.

Geologic Information

Map of the San Rafael Swell with access roads and many slot canyons labeled around the edges.

Generalized map of San Rafael Swell and surrounding areas.

The Swell is a broad, kidney-shaped convex-upward fold of sedimentary rock that contrasts with the surrounding flat-lying rock layers of the Colorado Plateau. This elongated dome-like structure, known as an anticline, is roughly 75 miles long (extending northeast-southwest) and 30 miles wide. The limbs or sides of this anticline are not symmetric. The southeastern limb, called the San Rafael Reef, is steeply inclined to nearly vertical, in contrast with the more gently sloped western limb. The Swell formed in response to compressional forces in the Earth’s crust during the Laramide orogeny, a mountain-building event that lasted from 70 to 40 million years ago. During this interval, other areas in Utah were also uplifted, such as the Uinta Mountains to the north and the Waterpocket Fold in Capitol Reef National Park to the southwest.

After the anticline formed, the Colorado Plateau began rising around 23 million years ago during the Miocene Epoch. This regional uplift created a landscape subject to massive erosion. Over millions of years, running water and wind removed up to 8,000 feet of material from the crest of the Swell and left behind a showcase of slot canyons, towers, and cliffs. The oldest rocks (about 300 million years old) are exposed in the center of the Swell, surrounded by a ring of progressively younger rocks (ranging from 100 to 230 million years old). From oldest to youngest, the strata include mostly sandstones of Moenkopi and Chinle Formations, the Wingate Sandstone, Kayenta Formation, Navajo Sandstone and the Carmel Formation.

Block diagram with illustrated rock layers being pushed up to form the swell and it's exposed geologic layers.

Diagrammatic illustration of the structure of the San Rafael Swell. Because they have been partially removed by erosion, the uppermost rock layers are no longer continuous over the anticline.

Today, the Swell is a diverse desert landscape. The San Rafael Reef (the steep eastern flank of the anticline) contains many narrow, winding slot canyons, whereas the central part of the Swell hosts vast flat areas, cliffs, and towers. Remnants of human history can be found throughout the Swell as well and include indigenous rock art and more recent evidence of homesteading and uranium mining.

Slot canyons in the Swell offer a fantastic opportunity to admire geologic history. The steeply tilted beds showcase the rock layers like books on a shelf. Canyons here also exhibit honeycomb or “tafoni” weathering, a process that creates small cave-like features that pockmark the canyon walls. Each slot canyon tells a different story!

Exploring Slot Canyons

Located in the southern part of the Swell, Little Wild Horse Canyon is a well-known slot canyon hike and an excellent choice for non-technical canyoneering. The trail can be made into a loop hike by returning down through Bell Canyon. The loop hike includes slickrock and sandy terrain, narrow winding slots, and panoramic views.

Ding and Dang Canyons are a bit more difficult and require route finding through steep down-climbs. For more advanced and technical adventures, the Upper Black Box or Cistern Canyons are scenic options requiring expert rope and canyoneering skills.

How to Get There

Map of access roads through the Swell.

How to access Little Wild Horse Canyon and Bell Canyon

To access Little Wild Horse Canyon and Bell Canyon, travel west from Green River on I-70 to the junction with State Route (SR) 24 (exit 160). Head south on SR-24 toward Hanksville for about 25 miles. Near mile post 35, turn west onto Temple Mountain Road and travel about 5 miles toward Goblin Valley State Park. Turn left (south) onto Goblin Valley Road and travel about 6 miles to the junction of Wild Horse Road. Turn right and head west for another 5.5 miles to the marked Little Wild Horse trailhead and parking area.

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