Slumgullion Earthflow – Lake City, Colorado - Atlas Obscura

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Slumgullion Earthflow

This National Natural Landmark is one of the best examples of a “mass wasting” in the world. 


Designated as a National Natural Landmark in 1983, this relatively young and still active slide is a good example of a geomorphological process known as “mass wasting.” Mass wasting is very common across landscapes disturbed by man. Natural landslides and slumps are also fairly commonplace, relatively rapid events that occur in landscapes with steep slopes and unconsolidated sediments. But the Slumgullion Earthflow is a natural phenomenon that is rare because it is moving in super slow motion.

Centuries ago, a portion of the Lake City caldera broke off of Mesa Seco and started moving down the steep slopes of the Lake Branch of the Gunnison River. Unlike many other slides, this was a slow-moving mass of materials known as mass flow or earth flow. The flow is about four miles long. Around 700 years ago, the flow dammed the Gunnison River’s Lake Fork to form Lake San Christobal. Soon after the damming of the river, the flow stopped.

Around three centuries ago, another slide from the same headwall started moving downhill. It has undergone active movement ever since at a rate of about 20 feet per year. Active areas of the flow can be seen in the assortment of tilted trees. The more trees that are tilted, the more active the flow.

The name Slumgullion comes from two sources. It’s often used by miners when describing the clay and mud left in the sluice when separating gold from ore. It’s also the name of stew.

Because of its uniqueness, the mass flow has been thoroughly studied throughout the years. The flow is faster in the summer when water is available and slower during the winter. The flow rate is related to tidal forces from the moon as well as air pressure. Pressure decreases at night, slowing the flow, and increases during the day, increasing the flow. Even climate change has had an impact on the geological wonder. Higher temperatures have slowed the flow and may even cause the newer flow to stop in the future.

Cannibal Mesa and Deadman Gulch, both named after the Packer Massacre, sit on the edge of the mass flow. The slide itself was first identified by Alferd Packer when he described the massacre site as, “being on the side of a large landslide.”

Know Before You Go

The mass flow can be viewed from the top of Slumgullion Pass to just outside Lake City on Colorado 149. Numerous pullouts exist along the west side of the pass with information on the flow. The flow has a high concentration of aspens making fall the best time to view the flow.  Traffic is increased during this time and extra caution should be taken.

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September 21, 2020

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