Geophysical data have enabled construction of a Precambrian basement structure controur map of the North Park-Middle Park basin in northern Colorado. Seismic refraction, gravity, and magnetic data were used with available well control to delineate structural relief ranging from 13,000 feet above sea level in the adjacent mountains to 9,000 feet below sea level in North Park. The Spring Creek normal fault, which trends west-northwest across North Park, has about 6,000 feet of vertical displacement. A structural high, 10-15 mi wide and 6,000-feet amplitude, is present in the basin in southern North Park. Gravity data suggest that several thousand feet of sedimentary rocks underlie the Independence Mountain and Never Summer thrust faults.

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