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<br />0=1495 <br /> <br />. <br /> <br />the dam, lower strata of the Vermejo formation are present, but <br /> <br />nowhere at foundation level or below is coal present. <br /> <br />Two vertical fracture patterns are present in the area of the <br /> <br />damsite. The dominant pattern has a persistent trend of about N. <br /> <br /> <br />700 w. The intensity of fracturing varies along the dam axis. The <br /> <br />o <br />other joint pattern trends N. 42 W. and is much less evident. <br /> <br />A few faults are present at the damsite. The displacement is <br /> <br />slight, ranging from a few feet to less than 25 feet. <br /> <br />Two closely.spaced and narrow basalt dikes cross the dam axis <br /> <br />southeast of the main valley. No basalt sills were found below <br /> <br />foundation level during any investigation. <br /> <br />e. Reservoir ~eolo~y. The reservoir lies on the eastern <br /> <br />flank of a broad subsidence (syncline) known as the Raton Basin. <br /> <br />The subsidence occurred somewhat prior to, but mainly concurrent with, <br /> <br />the uplifting of the Sangre de Cristo Mountains. This activity, known <br /> <br />as the Laramide Revolution, occurred during the late Cretaceous and <br /> <br />early Tertiary time periods. As a result of the subsidence, strata <br /> <br />on each flank of the basin dip toward the center. The supply of <br /> <br />sediments was sufficient to continually fill the basin, and, con- <br /> <br />sequently, the strata thickens from the basin edges toward the <br /> <br />center. Beds of the Vermejo and Raton formations dip and thicken <br /> <br />gently westward from the dam site into the reservoir area and beyond <br /> <br />the center of the basin. <br /> <br />In the reservoir area, scattered faults with small displacement <br /> <br />are present. The displacement is usually less than 25 feet and <br /> <br />. <br /> <br />II-17 <br />