About 800 years ago, a large section of Mesa Seco on the edge of the Lake City caldera broke off and moved down the steep slopes of the mesa. Rather than a large slide of rock, which would be common in the steep Colorado Rockies, the material flowed down the hill, almost like a river. This river of rock, mud, and gravel was called the Slumgullion Mass Flow. It flowed about four miles into the Lake Fork of the Gunnison River over the next 100 years or so. Called the…
