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4-7 <br />holes and laboratory analysis of roof and floor materials, <br />the roof rock consists of gray to black shales of varying <br />harness and competence; floor rock consists of similar shales <br />in some places and a medium grained friable <br />sandstone elsewhere. The sandstone is fairly persistent and <br />generally underlies the shales where it is not in direct con- <br />tact with the Cameo Seam. <br />Analyses of the roof and floor rock at the Munger Canyon <br />site (in accordance with 30 CFR 783.14) are presented in <br />Tables 4.2-1 and 4.2-2. <br />Slope conditions on the south side of Munger Canyon are indi- <br />cative of the slumping which occurs after heavy rainfall and <br />snowstorms. Small rapid movements of largely unconsolidated <br />• material usually occur where fluvial erosion steepens a slope <br />until the material can no longer resist the force of gravity. <br />Alternate freezing and thawing of these unconsolidated materials <br />may also cause the localized slumping which is evident in a <br />small area due west of the mine area. This slope failure is <br />documented by the mine entries and the following drill holes: <br />7-27-9, 7-27-10, 7-27-11, 7-27-12, 7-27-14, 7-27-16, 7-27-17 <br />and 7-27-18. <br />Based upon these limited observations, the roof and floor rock <br />is fairly competent with scattered areas of spalling and minor <br />localized floor heaving. Overburden thicknesses in the Permit <br />Area vary from 0 to 1,500 feet (See Figure 4.3-10). <br /> <br />