9 March 2018
Friday fold: Raplee Monocline
Posted by Callan Bentley
Arizona State University’s Steve Semken is the source of this week’s guest Friday fold:
The fold here is an insider’s view of the Raplee Monocline, as viewed from a raft on the San Juan River in Utah. Steve describes it as
Beloved of geology textbook publishers everywhere.
Though monoclines out west are usually huge features (and thus hard to fit in a single photo unless you’re in an airplane), this is a nice image because it clearly shows the strata at different angles of dip on different portions of the structure. Thanks for sharing, Steve!
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.
For those who might be interested, the red rocks at river level are siltstones and mudstones of the Lower Permian Halgaito Formation, and they overlie the interbedded grey limestones, shale, and sandstones of the Upper Pennsylvanian Paradox Formation exposed in the monocline. Viewed from the west, the folded incised grey and red rocks resemble the geometric pattern of a Navajo rug, and the Raplee Monocline is actually located on Navajo Nation land.