Abstract

Relief of the Precambrian surface in the Salt Valley-Cisco area, Utah and Colorado, is on the order of 19,000 ft between the crest of the Uncompahgre uplift in Colorado and the adjoining Paradox salt basin in Utah. Steep gravity and magnetic gradients just SW. of Cisco, Utah, indicate that the buried structural front of the ancestral Uncompahgre uplift has a relief of about 12,000 ft in a relatively narrow zone. Magnetic and gravity data further indicate that a buried ridge or salient of comparatively strong magnetic Precambrian rocks extends southwesterly and westerly from the main structural front of the ancestral uplift, past Yellow Cat dome, nearly to Salt Valley. NW. and W. of the postulated salient the basement rocks are comparatively deeply buried and weakly magnetized, according to drilling and to magnetic and gravity evidence. Analysis of a 26-mgal gravity low over Salt Valley anticline indicates that the vertical extent of the salt core is about 8000 ft. A gravity low of 10 mgal over Tenmile graben is related to a small, deeply buried salt anticline that is probably a northwestward extension of the Moab salt anticline.

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