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John Hamrick January 16, 2001 • Page 3 The Brushy Basin member of the Morrison Formation is predominantly a varigaceous bentonitic mudstone interbedded with occasional thin, lenticular beds of coarse-grained sandstone. Based on drill-hole data the thickness of the Brushy Basin at Beaver Mesa is between 370 and 400 feet. The Burro Canyon Formation overlies the Morrison Formation and is 210 feet of white to light brown fluvial sandstone interbedded with green and maroon lacustrine siltstone and shale and occasional thin limestone bed. The Morrison and Burro Canyon Formations outcrop in the southwestern portion of Beaver Mesa. It is in this area that the sandstone aquifers of these formations are recharged. The strata on Beaver Mesa are relatively flat, dipping 1° to 3° to the northeast. Ground water migrates within the aquifers to the northeast towards John Brown and Lumsden Canyons where these formations outcrop and form the steep mesa walls. 'The Lumsden fault (Figure 1), located north of the Fack Rat Mine in Lumsden Canyon, is the only fault that has been mapped in the area. It is a normal fault trending N70W and dipping to the south. Displacement appears to be about 65 to 100 feet. • Phoenix (1959) found that exploration drill holes throughout the Uravan mineral belt suggest that the ore-bearing aquifer is for the most part unconfined. Confined ground water, however, has been encountered in synclinal struchzres where the overlying nearly impermeable Brushy Basin member has not been removed by erosion. A similar configuration can be expected for other water-bearing sandstone layers in the Morrison formation. Groundwater flow on Beaver Mesa tends to follow the northeast regional dip. The direction and rate is also controlled in part by irregularities within the sandstone bodies and local mudstone layers. Stream scouring at the base of the ore-bearing sandstone into the underlying mudstone may act as channelways allowing greater amounts of groundwater flow. Three prominent springs, Willow Spring, DP Spring and Pack Rat Spring occur on Beaver Mesa. Willow Spring flows from the lower part of the Burro Canyon at the base of a cliff. DP Spring flows from the base of the Burro Canyon Formation where it is cut by the Lumsden fault at the head of Lumsden Canyon. Here the Burro Canyon Formation is in contact with Brushy Basin mudstones, which act as a barrier to further ground-water flow. The Pack Rat Spring issues from a joint near the base of the "ore- bearing sandstone" just above the prominent red mudstone unit and below the gray mudstone unit. This joint strikes N65°W and dips 80°N.