Hagerman Fossil Beds National Monument - Environmental Factors

In the early 1970’s approximately 27,000 acres of BLM land west and north of the monument, formerly used for grazing, were converted to irrigated agriculture use. Water is pumped from the river reservoir through large diameter steel pumps up to the plateau. Originally two pump stations were installed and used, but in 1987 an extensive landslide from the cliff above destroyed the Bell Rapids station. Following that event, all of the water needed for crop irrigation is pumped up to the plateau by the remaining Fossil Gulch pumping facility.

A total of five major landslides have occurred. The first occurred about 1979, but documentation started only after a larger 1983 landslide. Additional landslides occurred in 1987, 1989, and 1991. Another movement of the 1987 slide occurred in April, 1993. The slides are caused by the accumulation of irrigation water in the upper portions of the cliffs on top of impervious layers. Eventually these perched aquifers intersect the cliff faces and create seeps, some with flowing waters. One seep discharges 120 gallons per minute (7,200 gallons per hour) out of the walls of the cliff. Eventually the water-laden sediments lose their cohesiveness and obtain an unnatural weight, causing landslides to occur.

The previous landslides continue to expand upslope and laterally from initial failure areas. Inevitable future land movements represent a potential threat to the fossil resources, the existing irrigation pipeline, and a serious life and safety risk to the monument’s visitors, employees, and researchers. This irrigation-caused soil erosion is the most significant immediate and long-term threat to the paleontological, natural, and cultural resources of the monument. Experts are evaluating the landslide dynamics and investigating ways to mitigate the resource damage.