Old Faithful, a cone geyser in Yellowstone National Park, became famous after the Washburn–Langford–Doane Expedition named it in 1870 for its regular eruptions. First encountered on September 18, 1870, in the Upper Geyser Basin, it later became part of the Old Faithful Historic District with the nearby inn. Though not Yellowstone’s tallest or largest geyser, it is the park’s most celebrated for predictability, usually erupting about every 92 minutes and sending thousands of gallons of boiling water high into the air. Scientific studies, especially after the 1983 Borah Peak earthquake altered eruption intervals, have deepened understanding of the geyser’s underground system without diminishing its reputation.