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6 <br />• measured. Our mapping program has been performed without <br /> using accurate surveying; the accuracy of the map is there- <br /> fore limited. <br /> 2.4 ROCK STRUCTURE <br /> As part of the mapping and documentation program, <br /> measurements of the orientation of the joints have been made. <br /> Data on the joint orientations (rock structure) were not <br /> available from previous studies; they are of importance for <br /> the evaluation of the stability of cuts in rock. <br /> Joint measurements were made at four locations (sections) <br /> at the site. Section 1 is the west part of the rock cut above <br /> the diversion channel. Section 2 is the rock cut between the <br /> fan level and the portal level; measurements were made at <br />• elevation approximately 7,375 feet. Section 3 is the road cut <br /> between the office and crushing levels; measurements were made <br /> in the Rollins Sandstone. Section 4 is a road cut above the <br /> road switchback between the fan and portal levels. <br /> The results of the joint measurements are presented in <br /> the form of spherical projection plots which have been evalu- <br /> ated by using a computer program. The method of spherical <br /> projection and the computer analysis are described on Plates <br /> 3A and3B. <br /> The results of the analyses of individual wections are <br /> plotted on Plates 4 A through 4 D. Plate 4 E is :~ composite <br /> diagram of all measurements from all four sectic~~s. <br /> All rock structure diagrams show clearly Litat most of <br />• the joints are vertical or subvertical. There is one set of <br /> ccoeraocaau~.wc. <br />