It differs fundamentally in its composition, origin, and age from the volcanic rocks composing Mount Washburn. Tens of rhyolite lava flows were erupted one after another in central Yellowstone. Canyon Village is built on one. Elephant Back Mountain, west of Lake Hotel, is another. Several flows make up the plateau between Canyon Village and Norris, and several more bound the western margins of Yellowstone Lake.
Many streams follow seams between flows of different ages.
Lava flows can be readily dated. They contain various radioactive elements which decay to form daughter products. By measuring the relative amounts of parent material and daughter products and knowing the rate of change from parent to daughter, a geochronologist has a radioactive clock for dating the ages of flows. Between the Washburn Range and the Red Mountains, lava flows range in age from about 500,000 years to 100,000 years. To summarize, the Washburn Range is made of debris flows preserved in the north flank of an old dissected volcano.