Giantess Geyser, Geyser in Upper Geyser Basin, Yellowstone National Park, Wyoming, US

Giantess Geyser is a fountain-type geyser in the Upper Geyser Basin of Yellowstone National Park and features a large deep pool with boiling water at its center. The pool's edges are lined with thin mineral deposits that shift with each eruption.

The geyser was documented during the Washburn-Langford-Doane Expedition of 1870 by Walter Trumbull, who recorded its characteristics and eruption patterns in detail. This early observation helped scientists better understand Yellowstone's geothermal systems.

The name Giantess was given during the Washburn–Langford–Doane Expedition of 1870, when Walter Trumbull and Nathaniel P. Langford described the geyser's five jets rising from a vase-like pool. Langford called it the greatest wonder of the trip. Visitors still watch the crater for the pre-eruption rise and splashing.

The geyser erupts between two and six times yearly, shooting water up to 200 feet high. Eruptions can last from several hours to about 2 days, so follow ranger predictions to time your visit.

Walter Trumbull, on the 1870 Washburn expedition, noted that Giantess erupts as five jets: a main column about two feet wide that holds together for over 150 feet, with four smaller jets shooting higher. Nathaniel Langford, on the same trip, counted five lesser jets rising to 250 feet.