The Ski with a Ranger program is a one-hour guided tour that takes place on Fridays at Keystone. The tour starts at the top of the River Run gondola on Dercum Mountain. This activityÂ is free, but a lift ticket is required to ride up the gondola. Ranger-led topics include local history, wildlife and avalanche awareness. No reservations are required â just show up with your desire to learn something new about the mountain resort and surrounding areas. At least an intermediate skiing ability is required.