Geology of the San Rafael Swell

The San Rafael "swell" is actually an anticline - a huge dome formed by pressure from underneath the earth's surface. It is 80 miles long and 35 miles wide. Much like the way an accordion would be pressed together, this anticline manifests itself on the surface with striking ridge-like rock formations. More than 70 million years old, the San Rafael Swell shows how wind, water and changes from beneath the earth can shape a landscape. View this pdf chart showing the rock strata. Zoom in to get a clear look at what interests you.

The spectacular San Rafael Reef dominates the eastern side of the Swell. Erosion has exposed the jagged, upturned Navajo sandstone and cut deep canyons. These canyons are ideal for hiking and exploring.

Just one visit to the San Rafael will reveal a kaleidoscope of colors splashed across rugged cliffs, canyons and arches. Erosion sculpts the stone, but the environment during deposition determines its color. Generally, brighter colors including red, yellow and orange are apparent in rocks deposited where oxygen was present. Examples of these environments are sand dunes and floodplains higher than the water table. Dull colors, including gray, light green and purple are the result of deposition with no oxygen present, possibly at the bottom of an inland sea or below a water table. Such places also preserved the bones and footprints of dinosaurs.

The Cleveland-Lloyd Dinosaur Quarry is located in the northeast corner of the swell. It is one of the foremost sources of dinosaur fossils and the world's primary source of the flesh-eating Allosaur dinosaur. Take a tour of the quarry and visitors canter.

The climate of this area during prehistoric times ranged from Sahara-like deserts to small oceans and lush rivers. Now in this harsh arid region visitors will be surprised to find that certain types of vegetation flourish. Pinyon-juniper woodlands and open grasslands cover higher elevations; shrubs and grasses flourish at lower elevations and riparian species thrive along the river and canyons. North-facing alcoves and slopes are dotted with Ponderosa pine and Douglas fir.

Vegetation supports wildlife such as antelope, big horn sheep and mule deer.