Devil's Slide is a prominent cliff formation on Cinnabar Mountain in Montana, north of Yellowstone National Park, recognizable as two long, nearly vertical rock bands descending the mountainside. It formed when layers of limestone, sandstone, and quartzite were tilted almost upright and then eroded unevenly, leaving harder rock standing out as parallel walls. The Cook–Folsom–Peterson Expedition passed the site in 1869 and recorded it without naming it, and the Washburn–Langford–Doane Expedition applied the name in August 1870. Nathaniel P. Langford's 1871 account helped make it well known as a distinctive geological landmark tied to the region's early exploration.