THE ULTIMATE GEOLOGY FIELD TRIP: MISSOULA FLOODS TO HEART MOUNTAIN DETACHMENT

Fifty years ago I was introduced to the geology near Red Lodge, Montana by geologic masters like Earling Dorf, Russ Dutcher, Willard Parsons, and Don Wise. I returned in the early ‘70s with field trips from North Carolina State University, and in the early ‘90s to teach a course for the University of Pittsburgh. Realizing that many questions remained, in 1994-7 I directed Keck Geology Consortium projects to northwestern Wyoming. A result was one of the textbooks, East of Yellowstone: Geology of Clarks Fork Valley and the Nearby Beartooth and Absaroka Mountains, for my annual spring semester course on the Greater Yellowstone Ecosystem.

En route from eastern Washington we discuss the view from a kipuka (Steptoe Butte); examine Lake Missoula landforms and sediments; visit a silver, gold, or platinum mine in northern Idaho or southwestern Montana; and tour Lewis and Clark Caverns in the Madison Limestone. On the return we explore the Tetons, Earthquake Lake, Island Park Caldera, St. Anthony dune field, the Teton Dam site, Menan Butte tuff cones, and Craters of the Moon.

Clarks Fork Valley, the adjacent Bighorn Basin, Yellowstone National Park, and the Beartooth and Chief Joseph highways have rocks of every geologic period except the Silurian, starting with the 3.4 GA gneiss at Quad Creek. The rocks are plutonic, volcanic, metamorphic, and sedimentary, with Cambrian, Devonian, Permian, Jurassic, and Eocene fossils abundant. Landforms of mass wasting, fluvial, glacial, and periglacial origin are diverse and widespread, together with tectonic, volcanic, weathering, karst, and eolian features. Geologic highlights include a >2-billion-year nonconformity, tors and patterned ground at Beartooth Pass, Dead Indian Hill’s sackung in the Tensleep Sandstone, subaqueous moraines in Sunlight Basin, jokulhlaups from Glacial Lake Sunlight and other ice-dammed lakes, postglacial gorges, and carbonate breccia and rootless dikes of the Heart Mountain Detachment. Does anywhere else on Earth have such great geologic variety in such a small area?