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I I I I I I I I I I ,I il ,I I I I I I I -~- ._-~~- 4-1 SECTION 4. INVESTIGATIVE PROCEDURE 4.1 Review of Geological literature A comprehensive review of published and unpublished geological literature relative to the Study Area and the pertinent part of the Front Range has been completed. Particular attention was given to published data on Boulder County, the northern Front Range, and references to the lyons, Satanka, Ingleside, Fountain, and Silver Plume Formations. Cited references are listed at the end ,of the report in Section 7. 4.2 Topographic Mapping landmark Mapping of lakewood, Colorado, was retained to do ground control work, to fly the Study Area, and to present stereographic pairs of natural co lor aer i a 1 photographs of the Study Area. The exposure date of these photographs is December 5, 1981. The photographs were printed at an approximate scale of 1 inch equal to 600 feet and the photos were used to construct detailed topographic maps (8 sheets) at a scale of 1 inch equal to 100 feet with a contour interval ~~~e~ These maps were used as bases for( ~ all geologic mapping, the drafting of geologic cross sections, and the ~ plotting of geophysical traverses, drill holes, and jOint sllrvey locations. Infrared color aerial photographs also have been acquired, but were not available in time to contribute to this study. ''J! t ~ . J 4.3 Geologic Mapping Both photographic interpretation and on-the-ground field procedures were utilized in the geologic mapping process. The geologic maps represented by Plates 1 through 8 are our interpretations of geological conditions as indicated by (a) limited drillir.g and geophysical work at the dam site and (b) surface conditions noted in the Study Area as a whole. In many areas stratigraphic relationships and geological structure are masked by heavy vegetative cover and/or relatively thick soil cover. This is especially true in the geologically complex, proposed south abutment area of the dam. Accordingly, detailed subsurface investigation in some areas may reveal that geological conditions are significantly different than those indicated on our existing maps. Nevertheless, it is felt that our maps are suitable for the purposes of this report and that the conclusions of this report can be substantiated. UEBLACKER ASSOCIATES. INCo