San Juan River at Raplee Monocline

February 13, 2012


Photographer: Thomas McGuire
Summary Author: Thomas McGuire

The San Juan River cuts through the Raplee Monocline a few miles upstream from the settlement of Mexican Hat, Utah. Rock folds that dip in one direction are called monoclines of which there are many on the Colorado Plateau. It likely formed as a result of hidden, sub-surface compressional faulting, caused by the collision of the North American and Pacific plates, about 65 million years ago. The rock beds exposed here are part of the Hermosa group of Pennsylvanian age rocks. They're approximately 300 million years old. Oxidation of iron in some of the sedimentary layers gives them a reddish color.

Inflatable rafts can be seen in San Juan River in the above photo. When Lake Powell is high, those seeking a wilderness adventure can float down the river through the Goosenecks of the San Juan and into Lake Powell -- when the lake is low, dangerous rapids make this a perilous passage. Note the green, riparian vegetation (vegetation found along the rivers and stream). It's here that trees and other relatively deep-rooted plants in this desert environment are able to find sufficient groundwater to sustain growth. Photo taken on May 17, 2008.

Photo Details: Camera Maker: FUJIFILM; Camera Model: FinePix S9000; Focal Length: 11.7mm; Aperture: f/5.6; Exposure Time: 0.0025 s (1/400); ISO equiv: 80; Software: Adobe Photoshop Elements 9.0 Macintosh.