A large block of earth on the north side of Green Mountain has been moving downslope since the spring of 1998. Several luxury homes, costing as much as $600,000 each were built on the block in the past year or two. Three of the homes have now been declared unsuitable for habitation because of structural damage and torn gas and water lines. The properties are a "total loss" to the homeowners.    
   
   

Figure 1.  The driveway of the home in the middle of affected area is buckled and has cracks several inches wide. The yard of the same home has a foot-high offset along the margin of the main landslide block. On the south side of this home, the sidewalk has a pair of cracks, one of which is more than 30 feet long.

Figure 2.  Note large crack in the street.

The lower rocks on Green Mountain, called the Denver Formation, are claystone, siltstone, sandstone, and conglomerates, and it is within the Denver Formation that numerous landslide blocks have been mapped by Glenn Scott of the USGS (USGS Map I-790-A and I-790-B), especially where the mountain slope exceeds 15 degrees. The total thickness of the Denver Formation is about 950 feet. Sand and gravel deposits exist at the top of Green Mountain, and these deposits may be up to 650 feet thick. Small patches of younger sand and gravel were also mapped an the north side of Green Mountain by Scott in 1972. These materials were left behind by streams that flowed from the mountain front in the past few million years. Along the South Platte River, similar deposits are mined for sand and gravel.

Glenn's maps show large areas of landslide material on all sides of Green Mountain, including the area where homes on Bayaud Drive in the Sixth Avenue Estates were built. In addition, a map prepared for Jefferson County and Lakewood also identified the area as "an inactive landslide, unstable slope." These studies forced the County to zone the area off-limits to development until August 1990 when the Board of Commissioners changed the zoning in response to pressure from a developer.

Figure 3.  Geologist Standing In Large Crack on Green Mountain. Cracks above the damaged homes are one to two feet wide in places and several feet deep. Landsliding on the north side of Green Mountain is manifested by large cracks on the side of the mountain.

A digital geologic map of the Front Range, being prepared as part of the Front Range Infrastructure Resources Project, extends from the Castle Rock area on the south to north of Fort Collins, and includes the Green Mountain area. Use of the digital geologic map of the Front Range will provide planners and other decision-makers with geologic information that they can use in their geographic information systems and decision support systems.

U.S. Department of the Interior, U.S. Geological Survey URL: http://rockyweb.cr.usgs.gov/frontrange/virtour/greenmtn.htm Contact: Carol Mladinich  mailto:csmladinich@usgs.gov Updated: 05/16/2001