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Whirlwind Mine Groundwater Characterization Report <br /> may also contain slump features and piping cavities from infiltration of surface <br /> water. <br /> • Salt Wash Member. Regionally, 250 to 350 ft thick, consisting of interstratified <br /> lenses of lenticular very-fine to fine- grained sandstone (about 60%) <br /> interbedded with green and maroon mudstone (about 40%). Locally, the Salt <br /> Wash Member is in excess of 300 ft thick. This unit forms a ledgy slope with <br /> ledges consisting of white to light gray, gray-yellow, or light brown to rusty red <br /> fine to medium-grained sandstone. Sloped areas contain the interbedded <br /> mudstone units. The Salt Wash may have several prominent sandstone units, <br /> the top-most of which is referred to as the Top Rim, which hosts the ore <br /> deposits on Beaver Mesa. A similar thick sequence of sandstone near the <br /> bottom of the member is referred to as the Bottom Rim. Middle sandstone units <br /> may be referred to as the Middle Rim. Both the Middle and Bottom Rim <br /> sandstone units also locally host uranium/vanadium deposits. The third <br /> sandstone from the base (third rim or Top Rim sandstone) is typically the ore- <br /> bearing zone and is from 30 to 105 ft thick. As indicated by (Eicher and others, <br /> 1957), most mining and prospecting in the Beaver Mesa area has occurred <br /> within the Top Rim sandstone (see Figure 4). <br /> • Summerville Formation (Js); Jurassic; Regionally, approximately 110 ft thick, locally <br /> approximately 90 ft thick(Cater, 1955). Locally, the Summerville Formation, and <br /> possibly the lower Tidwell Member of the Morrison Formation consists of red-brown, <br /> thin and evenly bedded mudstone and shale and some light-gray, light-brown fine <br /> slabby grained sandstone. Locally, thin beds of red and green chert are common. <br /> • Entrada Sandstone; Jurassic; Regionally 200 to 310 ft thick. Consists of Dewey Bridge, <br /> Slick Rock and Moab Sandstone Members, mostly red-brown, white, buff horizontal <br /> beds of siltstone, mudstone, and fine to very fine-grained sandstone; Slick Rock <br /> Member is orange, buff white massive fine- grained sandstone of eolian origin; Moab <br /> Sandstone Member is red to gray fine to very-fine-grained sandstone. The Entrada <br /> Sandstone typically forms prominent red-brown rounded cliffs. <br /> Western Water& Land, Inc. 8 <br />