Potholes in Red Rocks Park
September 03, 2003
Potholes are testaments to the power of running water and the sediment it carries. The one that I'm standing in was carved by an ancient river out of a red sandstone formation near Morrison, Colorado. It's part of an awesome array of tilted red sandstone ledges in Red Rocks Park. Nestled in the foothills of the Rocky Mountains, some fifteen miles (23 km) west of Denver, the park’s sandstone monoliths are part of the Fountain Formation -- a sandstone of Pennsylvanian age that crops out along the Front Range in Colorado.
Most of the Fountain Formation can be called an arkrose -- a coarse, feldspar-rich sandstone that's typically pink in color because of the abundant pink feldspar grains within it. The formation was deposited by alluvial fans and braided streams draining off a nearby mountain uplift some 290-296 million years ago. Much of Central Colorado was uplifted during this mountain-building event, which occurred about 230 million years before the modern Rockies were raised. Subsequent uplift then slowly raised the great sandstone ledges at Red Rocks Park. Some of the rock formations in the park slope as much as 90 degrees, while others tilt backwards.