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1.3 Mapping Methods <br />It was determined that the most rapid, accurate, and economic method to <br />evaluate ground stability would be to make a photogeologic evaluation of 005 <br />Gulch and vicinity, followed by a field examination of the area using the <br />photogeology as a basis for additional detailed mapping. The photogeologic <br />evaluation was made of color aerial photography provided by Peabody Coal <br />Company. The aerial photographs were at the nominal scale of 1"=1000' and were <br />flown on June 30, 1990. <br />Two map scales, 1"=100' and 1"=400', were used in this investigation. This <br />necessitated the enlargement of geologic data plotted on the aerial photographs <br />by factors of X10 and of X2.5, The most accurate plotting medium available was <br />United States Geological Survey orthophoto quadrangles at the scale 1"=2000'. <br />The geologic data annotated on the aerial photographs were plotted to the <br />orthophoto quads and then enlarged in steps to maps at 1"=400' and 1"=100'. <br />Although there are inaccuracies in transferring data through such a broad range <br />of scales, checks of the method used indicated a sufficient level of accuracy <br />for the purpose of this investigation. <br />Peabody Coal Company (PCC) provided reproducible films of the following <br />maps on which geologic data were plotted; drawing numbers in the Amuedo and <br />Ivey title blocks indicate the numbers assigned specifically to this <br />investigation. The following maps accompany this report. <br />a) Drawing No. 9111-1 Regional Geology, PCC Topographic Map, scale <br />l"=400'. <br />b) Drawing No. 9111-2 Regional Geology, PCC Operations Map, scale <br />1"=400'. <br />c) Drawing No. 9111-3 Haul Road G, Surficial Geology (Sta. 0+00 to Sta. • <br />32+00), PCC Exhibit 13-19.1, scale 1"=100'. <br />2 <br />