The Hardrock 100 is considered one of the most difficult ultra marathons in the world. Each year, hundreds enter a lottery for a little bit less than 150 spots. Many will finish the 100.5-mile course in the San Juan Mountains, which loops runners from Silverton to Telluride, Ouray, Lake City and back within the 48 hour time limit, but many others will not. Storms, rain, snow and sprained ankles are all common. Runners gain roughly 33,000 feet over the course and descend another 33,000. Below are a collection of photos on the course: