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• The clays and clay-shales found in the Laramie Formation can be defined as uncemented or weakly cemented, overconsolidated clays generally exhibiting the following properties: 1. low strength. 2, hea swelling and shrinking potential with increases and decreases in moisture content. 3. has a tendency to "slake" (decompose) when exposed to air and water. 4. has a high compressibility under intense loading. 5. and is prone to differential weathering. The properties of clay shales in the mining Brea can be largely attributed to their geologic history. Clay mineral content, lithologic variations and bedding are primarily linked to their depositional history, while secondary features such as jointing, alickened aides, fissures, end faulting are mainly a result of the stress history. Chemical and physical alteration due to exposure and weathering tend to modify these primary and secondary features, creating a zone underlying the eolian sand deposits that has variable engineering properties. • From the analysis of core retrieved in the area, occasional zones (usually 2" - 6" in thickness) of stained/altered clays were discovered at depth. These are probably remnants of materials that were, at one time, exposed at the surface. Such layers would be potential zones of weakness, however, because orientations are nearly horizontal, they would not be considered a condition of potential failure by themselves during mining activities. From observations of the Laramie Formation at the Keenesburg Mine CSec 25, T3N, R64W) and core obtained during exploration activities in Sec. 17,T3N, R63W, the clay-shales exhibit a condition of stress release within the formation. Slickened slides or "micro-faults" have very random orientations and are generally continuous for only a few feet. Joint patterns have also been observed in nreas of stress due to minor warping and buckling of the Laramie formation clays. These joint patterns have been traced in the A-Pit highwall at the Keenesburg Mine and can be up to 35 feet in length. Displacements along these near vertical failure planes are typically O' - .5', but have been observed to be 5' - 15' in areas of more intense fnulting. Aa a result of weathering, three zones occur within the clay-clay shale sequence of the Laramie Formation. The first zone, which underlies the unconsolidated eolian sands, • consists primarily of a disintegrated, oxidized and weathered material generally O' - 10' in thickness, usually silty and sandy in nature. -9-