The Crooked River caldera is a 26-mile long, 17-mile wide volcanic depression formed through a series of super-volcanic eruptions between 29.7 and 27.5 million years ago. Eruptions from the Crooked River caldera deposited massive volumes (>140 cubic miles) of tuff and rhyolitic lavas, dikes, and domes. All of these volcanic features are now well exposed in the rock walls of Smith Rock State Park.
Current research suggests that the Crooked River caldera records some of the oldest caldera-forming eruptions related to the passage of the Yellowstone volcanic hotspot from the coast of the Pacific Northwest to the modern Yellowstone caldera in Wyoming during the past 50 million years. The Crooked River caldera also contributed a significant amount of volcanic material to the Turtle Cove Member of the John Day Formation, which hosts one of the world’s most complete and well-preserved fossil records of Cenozoic terrestrial plants and animals.
This field trip will be led by Jason McClaughry from the Oregon Department of Geology and Mineral Industries. The trip is appropriate for all levels of geologic background, but will emphasize in-depth discussions of the volcanic processes that created the Crooked River caldera.
Total walking distance will be less than 2 miles, mostly on flat terrain but some stops may include short walks over uneven ground.
Additional materials and background information:
McClaughry J.D., Ferns, M.L, Gordon, C.L., and Patridge, K.A. (2009). Field trip guide to the Oligocene Crooked River caldera: Central Oregon’s Supervolcano, Crook, Deschutes, and Jefferson Counties, Oregon. Oregon Geology, Volume 69, No. 1, pp. 25-44.
McClaughry J.D. & Patton, P. The Oregon Encyclopedia: Smith Rock State Park.
Central Oregon Geoscience Society
P.O. Box 2154, Bend, Oregon 97709