2020-02-07_REVISION - M1977211 (14)

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1100318 R0T0 0811 JRW1 22 unit; the uppermost of these was encountered approximately 8 feet below the top of the unit in boring EXC-2. This clay bed, which is approximately 2 inches thick, was encountered at a depth of 80 feet in EXC-2 (drilled on the floor of Area H) and is interpreted to represent the principal plane of weakness in the slope and the locus of sliding of the Pikeview Landslide and major episodes of post-December 2, 2008 landslide movement. The upper member of the Sawatch Formation is exposed locally near the western margin of the quarry, immediately east of the Rampart Range Fault, where near-vertical outcrops are present in the north graben area (see geologic map, Appendix 39). The Sawatch Formation grades transitionally upwards into the basal Manitou Formation (Lower Ordovician age), designated as unit Omb on the geologic map and cross sections presented in Appendix 39. From the top of the Sawatch Formation, the basal Manitou Formation consists of variable thicknesses of calcareous sandstone, sandy limestone, and predominantly red limestone. The basal Manitou Formation measures approximately 35 to 40 feet in thickness. This unit is exposed locally near boring EXC-3 on the floor of Area H and also near the south end of Area H, as shown on the geologic map (Appendix 39). Much of the northerly portion of the toe of the December 2, 2008 landslide is composed of red limestone of the basal Manitou Formation. The basal Manitou Formation is overlain by the Manitou Formation (Lower Ordovician age), indicated on the geologic map and cross sections (Appendix 39) by the unit designation Om. The Manitou Formation consists predominantly of white limestone, frequently with dark red mottling, alternating with light brown and light red intervals. The Manitou Formation is the principal mined unit at the Pikeview Quarry. It is the strongest unit in the quarry and can only be mined by drilling and blasting. It is locally rich in chert (a silicate mineral), rendering the unit particularly strong in the southern part of the quarry (in the vicinity of EXC-4; see geologic map in Appendix 39 for location). The Manitou Formation also locally exhibits cavernous weathering, particularly in the vicinity of the Rampart Range Fault, with cave openings present near the southern end of the Permit Area. The unit exhibits a locally chaotic texture in two locations, in the vicinity of boring EXC-3 on the floor of Area H, as well as in the amphitheatre- shaped region at the south end of the quarry. Exposures of the bedrock textures in the latter area suggest that the chaotic texture in this area reflects the presence of an ancient submarine