Mount Adams, Stratovolcano in Cascade Range, Washington, US.

Mount Adams is an andesite stratovolcano in the Cascade Range of Yakima County, Washington. Glaciers such as Adams and Klickitat stretch across the slopes, carving deep valleys between the ridges that descend from the summit.

Mount Adams began forming in the Pleistocene, with minor activity from about 900,000 years ago and major cone building from roughly 520,000 years ago; the modern cone took shape around 10,000 years ago. Its last known lava flow was about 1,000 years ago, around 950. The name came by accident: in the 1830s Hall J. Kelley planned to rename Cascade peaks after presidents, and mapmaker Thomas J. Farnham placed "Mount Adams" on an unnamed mountain; it became official in 1853 under Isaac I. Stevens. The first recorded ascent was in 1854.

Yakama communities maintain a deep connection to the peak, known as Pahto in their language, and weave it into creation stories as a brother to other Cascade summits. Hunters and gatherers have used the mountain flanks for centuries as seasonal routes and harvesting grounds for berries and wild plants.

Hikers planning an ascent should monitor weather conditions closely, as storms can develop rapidly. Gear for glacier travel and an early start help avoid crevasses and afternoon snowfall.

The summit area is nearly flat, its central crater filled with snow and opening westward, ringed by rock pinnacles such as The Pinnacle, The Castle and Piker's Peak. These formed through glacial erosion and the nesting of several older craters. Near Trout Lake, lava tubes called the Ice Caves hold snow and ice stalactites at their entrances.