The West Thumb Geyser Basin, including Potts Basin to the north, is unique in that it is the largest geyser basin on the shores of Yellowstone Lake. The heat source of the thermal features in this location is thought to be relatively close to the surface, only 10,000 feet down! The West Thumb of Yellowstone Lake was formed by a large volcanic explosion that occurred approximately 150,000 years ago (125,000-200,000). The resulting collapsed volcano, called a caldera ("boiling pot" or caldron), later filled with water forming an extension of Yellowstone Lake. The West Thumb is about the same size as another famous volcanic caldera, Crater Lake in Oregon, but much smaller than the great Yellowstone caldera which formed 600,000 years ago. It is interesting to note that West Thumb is a caldera within a caldera.

Stroll through a geyser basin of colorful hot springs and dormant lakeshore geysers situated on the scenic shores of Yellowstone Lake. Trails and boardwalks are handicapped accessible with assistance.