Slumgullion Earthflow is an excellent illustration of the geologic process of mass wasting. Seven hundred years ago, a huge mass of volcanic rock slumped from the mountainside and flowed into the main valley where it spread laterally to form Lake San Cristobal. The older flow is presently being overridden by a new flow moving up to 20 feet per year.
Year designated: 1965
Ownership: Federal, Private
Please remember, National Natural Landmarks (NNLs) are not national parks. NNLs are owned by a variety of public and private entities and allowing visitation is at their discretion. Many NNL sites maintain public websites where additional information may be found.