2020-03-30_HYDROLOGY - M1981021 - Laserfiche WebLink

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SUNDAY MINE COMPLEX-HYDROGEOLOGIC REPORT observed in the Grand Canyon to the south. Lowe (1996) reports that the Leadville Limestone underlies all of San Juan County in southeastern Utah. The oldest formation that outcrops in the local area is the Pennsylvanian Hermosa Formation. The lower member of the Hermosa Formation, the Paradox member, is comprised primarily of intrusive salt and gypsum. During drilling activities in Paradox Valley, the Paradox member has been found to be more than 10,800 ft thick and to contain over 50% salt. In places where the Paradox member outcrops, the salts are dissolved and only gypsum remains. The dissolution of these salts in groundwater is believed to be the primary cause of the collapse features and complex faulting area. The upper member of the Hermosa Formation is fossiliferous thick- bedded gray limestone interspersed with shale lenses. Nearby boreholes have shown this member to be 2,000-2,300 ft thick. The Permian Cutler Formation overlies the Hermosa Formation and consists of maroon, red and purple conglomerate, and thin, irregular beds of arkosic sandy mudstone. The Cutler Formation nears 3,000 ft in thickness but outcrops only a few hundred ft at the mouth of Hamm Canyon on the northern slope of Big Gypsum Valley. The Chinle Formation of the Upper Triassic period overlies the Cutler Formation and is composed of red and orange-red siltstone interbedded with lenses of red sandstone, shale, and limestone-pebble and clay-pellet conglomerate. At the base of the formation conglomerate lenses contain quartz pebbles and grit. The formation is approximately 500-600 ft thick but thins along the flank of the Gypsum Valley anticline and outcrops at the base of the cliff wall on the northern side of Big Gypsum Valley. The Moenkopi Formation is not present in the vicinity of the SMC. The Jurassic Glen Canyon group consists of the Wingate sandstone, the Kayenta Formation, and Navajo sandstone in ascending order. The Glen Canyon group conformably overlies the Chinle Formation. The Wingate sandstone is composed of fine-grained reddish-brown quartz sand and typically outcrops in the form of massive cliffs forming walls with vertical joints throughout the wall. The Kayenta Formation is mostly made up of irregularly bedded red, buff, gray and lavender coarse-grained sandstone but also contains beds of shale, red siltstone and conglomerate comprised of sandstone, shale and limestone pebbles. The Kayenta Formation in the Big Gypsum Valley area ranges from 180-210 ft in thickness. The Navajo sandstone, which overlies the Kayenta Formation, is a buff to gray-colored, crossbedded sandstone. The Western Water& Land, Inc. 7