San Rafael Reef
The tilted-on-end eastern rampart of the San Rafael Swell — a 75-mile monocline of Navajo and Wingate Sandstone cut into fins and slot canyons.
The San Rafael Reef is the steeply upturned eastern edge of the San Rafael Swell — a 75-mile wall of tilted sandstone where the flank of the great dome bends sharply down toward the desert. Its layers of Jurassic Navajo and Wingate Sandstone stand nearly on end, eroded into a serrated line of fins, domes, and knife-thin slot canyons that Interstate 70 slices straight through. It is the monocline that gives the Swell its hard eastern boundary.
Geology
Formation: The steeply dipping eastern limb (a monocline) of the Laramide San Rafael Swell anticline, where the Mesozoic section flexes sharply downward and is eroded into hogbacks, fins, and slot canyons.
A classic Colorado Plateau monocline — the flexed limb of a basement-cored uplift — exposed continuously for ~75 miles and cross-sectioned by the canyons that drain the Swell.
Primary formation: Navajo Sandstone
Age: Paleogene (50 Mya)
The 60,442-acre San Rafael Reef Wilderness was designated in 2019.
History
A 'reef' in the old sense — a ridge that blocks travel; the tilted sandstone wall long barred east–west passage.