At 3:30 in the afternoon we were strapping in for our last run off the backside of Cougar Peak when we heard thunder from the north. We looked across the canyon in the north fork of Cherry Creek and witnessed a natural avalanche pouring off a cliff band. We continued to watch as the avalanche slowly snaked its way down the bottom of the canyon running a total of 1000 vertical (8500 down to 7500). The snow consisted of the saturated snow on a Southwest facing slope and came to a stop in a deep pile in the bottom of that canyon.