The oldest and hottest thermal area in Grand Teton National Park is also its most dynamic. While temperatures of 459ºF have been recorded just 1,000ft underground, the features of this basin have undergone regular fluctuations in temperature and activity. The major geysers are in Back Basin, where thermal features are scattered among trees. Steamboat Geyser is the world's tallest active geyser. Its rare major eruptions (it is dormant for years at a time) can reach heights of 400ft. Echinus Geyser, the largest acid-water geyser, puts on an entertaining show every 40-80min, filling, erupting and draining like a toilet bowl.