Big Slide Mountain is an Adirondack High Peak in Keene, northeastern New York, rising 4,240 feet and ranking 27th in height among the High Peaks. First recorded climbed in 1812 by surveyor John Richards while marking lot lines in the Old Military Tract, it took its name from major landslides recorded in 1830 and 1856. The mountain is especially valued as a hiking destination, with popular routes over the Brothers and others through Johns Brook Valley and Klondike Notch. Its broad views and summit outlooks toward the Great Range, Giant Mountain, and Algonquin Peak have made it a well-known objective within Adirondack Park.