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4202 . The Arkansas Valley Conduit will be constructed in an area which contains nearly horizontal Cretaceous-aged shales, sandstone, and limestone mantled with a few feet of over- burden. The Arkansas River and its major tributaries have valleys containing considerable thicknesses of alluvium. Dune sand occurs in an extensive belt along portions of the Arkansas Valley and in certain locales extends into the uplands. c. Seismicity Despite its mountainous interior, all of Colorado is con- sidered seismically stable (see Figure 111-7). No destruc- tive earthquake has occurred within its borders in recorded history. Minor earthquakes have occurred in all parts of the state, some of which were located, in or adjacent to the area encompassing the Fryingpan-Arkansas Project. Faults occur throughout the Fryingpan-Arkansas area; however, almost all are considered to be inactive. Displacement within unconsolidated deposits has been noted in the Upper Arkansas Valley (Tweto, 1961) and in the vicinity of Pueblo (Scott, 1970). The epicenter and intensity of recorded earthquakes are shown in Figure 111-8 and the approximate relationship between intensity, acceleration, and magnitude of the earthquakes are shown in Figure 111-9. . d. Slides and Shoreline Stability (1) Slides Evidence of ground movement within the project area is quite varied in type and size. Landslides of some consequence have occurred in two locations: Ruedi Reservoir and the Mt. Elbert Pumped-Storage Powerplant. Following are discussions of each. Ruedi Reservoir - Several small landslides of the nuisance variety have occurred at Ruedi Dam and Reservoir. Areas of the reservoir are in contact with steep slopes with varying-amounts of overburden. Shoreline erosion in locations where the overburden was several feet thick caused several small slides to develop. Their presence and "apparent" seriousness was accented by being formed III-IS .