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<br />0029~ <br /> <br />River Bluff Retreat - a case history <br />(Lamplite Park subdivision, Grand Junction, Mesa County, Colorado) <br /> <br />Introduction <br /> <br />The Lamplite Park subdivision is located in Grand Junction, Colorado on a <br />bluff overlooking the Colorado River (Fig. ___). <br /> <br />Identification of Landslide Hazard <br /> <br />The effects of the Lamplite slide were first noticed in the early 1980's, soon <br />after the development was completed. However, aerial photographs indicated <br />that a landslide had existed on the site as early as 1954. Photo analysis <br />showed that the head scarp had receded about fifty feet between 1954 and <br />1973. Investigation of the land-use history revealed that the site had been <br />used as a gravel pit, junk yard, and a clean-fill dump prior to development. <br /> <br />When the subdivision was proposed in 1976, the geotechnical report prepared <br />identified the slide and made several recommendations regarding construction <br />on the site; these included avoidance. The main part of the site was <br />developed by 1982. At that time, the property passed to a second developer <br />who built a row of houses on the north side of Santa Clara Avenue in the <br />immediate area of the head scarp. At this time clean fill dirt was trucked to <br />the site, dumped, and graded to level the backyards of these lots. <br /> <br />Within a year or so of construction at least two houses began experiencing <br />problems associated with differential movement. By November, 1984, these two <br />houses were condemned and the residents had filed lawsuits against the county, <br />city, and individuals involved with the construction. <br /> <br />Geologic Evaluation <br /> <br />The Lamplite slide is a complex rotational failure. The slide mass itself is <br />a relatively thin (10 to 20 feet thick) section of unconsolidated muds, clays, <br />sands and gravels of the Orchard Mesa terrace gravel deposit. The slip <br />surface is saturated, soft, extremely weathered shale. Bedrock is unweathered <br />Mancos Shale. The slip plane is lubricated by discharge from a perched water <br />table in the terrace gravels. <br /> <br />- 84 - <br />