Reader feedback on geology

Recently we heard from someone who found our article on Beartooth Butte confusing, so I revised that “Nugget” to be clearer. We describe a geological feature you can see if you drive outside the Northeast Entrance of Yellowstone National Park toward Red Lodge, Montana. The part we had to clear up is that Beartooth Butte is in Wyoming, but the Beartooth Range is almost wholly in Montana. The butte sits above a lake with the same name, about 20 miles on US Highway 212 from the state line.

Did you know that geologist Jo-Ann Sherwin and I spent a lot of time updating the geology in the latest edition of Yellowstone Treasures? This map we revised is the most technical one, not intended for navigation like most of the 38 maps in the guidebook! Besides the types of rock in the different mountains, the map shows calderas. (A caldera is a large circular or elliptical crater or depression formed by the collapse of a large land area after the emptying of a magma chamber in a massive volcanic explosion.) Notice how the most recent—and famous—Yellowstone Caldera is marked with a solid line because much of its edge is visible at the surface. Meanwhile, the Henrys Fork and Huckleberry Ridge Calderas have a dashed outline to show that the caldera edge is buried under more recent volcanics. East of the park, the dotted outlines of the Heart Mountain detachment and its remnants show their general size, shape, and location. These are large chunks of Paleozoic sedimentary rock that became detached from the underlying rock and slid to the southeast over the Bighorn Basin. There’s lots more to explain calderas and other geological formations in the guidebook’s Geological History chapter.

We welcome your feedback on either our books or this website. Contact us!
—Editor Beth Chapple

Map credit: Jo-Ann Sherwin adapted this map with permission from Mountain Press’s Roadside Geology of Wyoming, 2nd ed., 1991, by David R. Lageson and Darwin R. Spearing.

Elsewhere on this website you can read about “The Yellowstone Caldera” and the Heart Mountain Interpretive center: https://www.yellowstonetreasures.com/2013/07/14/trip-report-heart-mountain/.