Ypsilon Mountain is a 13,520-foot summit in the Mummy Range of Rocky Mountain National Park in northern Colorado, standing with Mount Chiquita among high peaks most easily reached from Fall River Road to the south. It received its name in 1887, when Mrs. Frederick H. Chapin chose it for the distinct Y-shaped snowfield on its east face, named after the Greek letter Ypsilon. The mountain is also known for its mountaineering and rock-climbing terrain. In 2023, it was the site of a fatal accident when climber Bailee Mulholland fell 500 feet while free-soloing the Four Aces of Blitzen Ridge.