Castle Geyser, a cone geyser in Yellowstone’s Upper Geyser Basin, is distinguished by the heavy geyserite sinter deposits that built a massive cone likened to a castle. The Washburn-Langford-Doane Expedition named it on September 18, 1870, after Lieutenant Gustavus Cheyney Doane saw in its upper edges the form of a keep with turrets and crenellations. Its shape has changed over time as eruptions added mineral layers, and modern scanning indicates four or five developmental stages. Carbon-14 dating places the present cone around 1022, much younger than earlier estimates. It erupts about every 16 to 17 hours, with a 90-foot water column followed by a prolonged steam phase.