The 1,400' climb has much to recommend it, including geology. Seen along the road is a dark breccia consisting of anglular volcanic stones, embedded in a fine angular matrix. This breccia formed some 50 million years ago when watery mixtures of ash and rocks flowed down mountain slopes onto then tropical lowlands. There are countless volcanic mudflows that make up the Washburn Range and mountains to the east. All were deposited over a period of 10 million years.
Bedding planes separating breccia layers are instructive.
In Mount Washburn and surrounding peaks, all slope northward. We search to the south for these flows in vain. Far below us is Washburn Hot Springs, the Grand Canyon of the Yellowstone, Hayden Valley, and Yellowstone Lake. The summits of Washburn and Sheridan are within 65 feet of each other in elevation. This range is a part of the Absaroka volcanic field, which also forms the mountainous terrain east of Yellowstone Lake.