Debris flows are a common hazard in many hillside areas of Colorado. Heavy rainfalls commonly trigger flash floods on steep slopes. These torrents pick up anything in their paths and may contain more solid material than liquid. They tear into the hillsides and deposit accumulated material when they reach flatter ground, creating an alluvial fan
A superlative alluvial-fan deposit can be viewed in Horseshoe Park in Rocky Mountain National Park. This deposit formed on a single day in July 1982, when the Lawn Lake Dam burst, sending a huge surge of water and debris down the Roaring River Valley.
Although alluvial fans may appear to be attractive building sites, it is prudent to remember that another debris flow may follow the same course that created this area. If it does, your new home may well end up a bit farther down the valley and flatter than you planned.