1142 Subsurface Geologic Methods 



appendix to the reconnaissance report and should include drill- and 

 test-pit logs, geologic cross sections when feasible, and outcrop or geologic 

 maps. The importance of such a map should be emphasized, for, al- 

 though an outcrop map is better than nothing, it cannot replace a properly 

 made geologic map. 



Stage C: Preliminary Designs and Cost Estimates 



The over-all purpose of stage C is to provide a basis for requesting 

 authorization and appropriation. Most of the main points relative to 

 stage C explorations are covered in paragraphs relative to stage B above, 

 but the stage C investigations are carried on with a view to providing all 

 data necessary for the preliminary design and estimate and are more 

 complete than those limited to the purpose of site selection. The purpose 

 of carrying out the steps necessary in stage C is to develop more 

 specifically the surface and subsurface conditions at the proposed loca- 

 tion of appurtenant structures, as well as at the main structure, and to 

 establish more definitely the character, quantity, and cost of construction 

 materials. The extent of stage C explorations will depend on the complete- 

 ness of stage A and stage B explorations, the complexity of subsurface 

 geologic conditions, and the importance of the structure. 



The preparation of an adequate geologic map again cannot be too 

 strongly emphasized. It should be one of the first steps in the stage C 

 exploration, especially if such a map was not prepared previously. A 

 geologic map should be made before or while topographic map is made. 

 The geologic map should show (1) contacts of overburden in bedrock 

 areas, contacts between types of overburden, such as slope wash, talus, 

 alluvial and glacial drifts, and landslides; contacts between kinds of 

 rocks in the outcrop area; and formation boundaries within outcrop 

 areas; (2) dips and strikes in sedimentary or metamorphic rocks taken 

 at frequent intervals; (3) geologic columns with detailed descriptions of 

 the sedimentary section if possible; (4) structural contours in sedi- 

 mentary rock where appropriate; (5) the physical condition of the rock 

 exposed, as shattered, crushed, sound, hard, or soft, and the degree of 

 weathering; (6) a surface trace of fault planes or zones, the amount 

 and direction of displacement, and the effect on the attitude and condition 

 of rock; (7) the prominent joint systems, directions, spacing, and effect 

 on rocks; (8) the estimated thickness of the overburden where this has 

 not previously been determined by drill holes and test pits, which are 

 to be shown by figures and circles on maps; (9) the lines of geologic 

 cross sections; (10) the location of all drill and auger holes, exploration 

 tunnels or shafts, and test pits; and (11) a legend or explanation using 

 formation or rock symbols or conventional signs. 



Stage C explorations should be suflSciently complete to permit the 

 development of geologic cross sections. 



