About 850 years ago the mountainside let loose and a yellowish mud slid for about 4 miles blocking off a part of the Gunnison River and forming Lake San Cristobal, Colorado's second largest natural lake. Because of its unique geologic history, this earthflow has National designation and is still flowing today.
If you drive on the Silver Thread Scenic Byway (Highway 149) between Lake City and Creede you will see the slumgullion mud everywhere.