Alluvial fan By Matt Young September 8, 2014 12:00 MST Alluvial fan created by the torrential rainfall 1 year ago, as seen from the Visitor Center, Trail Ridge Road, Rocky Mountain National Park, Colorado, September, 2014. The meander at the bottom of the screen passes through the bed of Fan Lake, which was formed in 1982 when the Lawn Lake Dam burst and inundated the City of Estes Park.