East Beckwith Mountain is a laccolith, formed when magmaintruded into Mancos Shale approximately 30 million years ago. Subsequently, the softer, overlying sedimentary rock has eroded away, exposing the more resistant igneous rock. East Beckwith Mountain is one of over a dozen laccoliths in the West Elk and adjacent Elk Mountains. Of these laccoliths, East Beckwith Mountain is noted for its distinctive glacial landforms. On the north side of this elongated, east–west oriented mountain, there are five glacially carved cirques with intervening arêtes, and moraines fan out from the mountain's base.[5][6]