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- 1 0 - <br />presently occur only where preserved in down faulted blocks along some <br />of the salt anticlines. Early Tertiary formations are widespread in <br />adjoining regions to the north and east. It is likely that these <br />formations at one time extended into the area; however, they have been <br />completely removed by subsequent erosion. <br />Surficial deposits in the region are generally thin. Cemented <br />gravels have been reported in the Paradox Valley, Cater (1970). He <br />believes that these gravels were deposited on the valley floor when it <br />was somewhat deeper than at the present time. In most places, the <br />cemented gravels are exposed only in washes which have been carved <br />through the more recent valley fill deposits. In the northwestern <br />part of Paradox Valley, lake beds overlie the cemented gravels. A <br />volcanic ash layer in the lake deposits has tentatively been <br />correlated with air fall deposits associated with the eruption of the <br />Bishop tuff in east - central California. The Bishop tuff has been <br />dated by radiometric methods as being about 700,000 years old, <br />Dalrymple and others (1965). The cemented gravels post -date the <br />collapse and subsequent erosion of the anticlines crest. The deposits <br />indicate that the topography of the valley had virtually reached its <br />present form by Late Paleocene or early Pleistocene time. <br />Alluvial silts and silty sands cover much of the Paradox Valley <br />floor and in places may be up to 100 feet thick. Thin colluvial <br />deposits overlie bedrock on the moderately sloping valley side. The <br />steeper valley sides are generally underlain by bedrock outcrops. <br />Landslide deposits are also common on the valley sides and are <br />usually associated with the upper portions of the Brushy Basin member <br />t <br />