Selected water-level data for Mesozoic formations in the upper Colorado River basin in Arizona, Colorado, Utah, and Wyoming; excluding the San Juan Basin

The base of the moderately saline water (water that contains from 3,000 to 10,000 mg/L of dissolved solids) was mapped by using available water quality data and by determining formation-water resistivities from geophysical well logs based on the resistivity-porosity, spontaneous-potential, and resistivity-ratio methods. The contour map developed from these data showed a mound of very saline and briny water, mostly of sodium chloride and sodium bicarbonate type, in most of that part of the Uinta Basin that is underlain by either the Green River or Wasatch Formations. Along its northern edge, the mound rises steeply from below sea level to within 2,000 ft of the land surface and, locally, to land surface. Along its southern edge, the mound rises less steeply and is more complex in outline. This body of very saline to briny water may be a lens; many wells or test holes drilled within the area underlain by the mound re-entered fresh to moderately saline water at depths of 8,000 to 15,000 ft below land surface. (Author 's abstract)