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I I I I I I I I I I I I I I I I I I I ..~ en ~the Conejos and Los Pinos Rivers. Evidence for this so far is indirect. (- ~Geophysical logs show limited continuity between highly conductive layers within the Conejos Formation from north to south. In addition, there appears to be a deficit of water in the sub-basins of the Rio Grande, and a surplus of water in the sub-basins of the Conejos River (Interim Task 2 Report, this study). At present, this should be considered only as an hypothesis, and not as a definite conclusion. Several known hot spring areas in and surrounding the Valley occur along lineations, interpreted to be faults, identified on satellite imagery. This is strong evidence of structural control on upwelling thermal waters into the aquifers of the Valley. These lineations, and the locations of the hot springs, have been verified through on-site geologic reconnaissance by study team members. It is felt that this conclusion is definite, and that further work would substantiate this conclusion for the Valley as a whole. Deep ground water in the San Luis Valley shows evidence of chemical evolution from a predominantly bicarbonate~rich chemistry near the basin- margin recharge areas, to a chloride-rich chemistry toward the center of the Valley. Mixing of ground waters due to upward movement of poorer-quality thermal waters through faulted areas apparently complicates the chemical evolution of the water, and, in most cases, degrades the water quality. These conclusions, which are considered to be quite definite for the rift-related faulted areas of the San Luis Valley, have been based on review of previous studies, on comparison with ground water evolution in other, better-documented basins, and on water-chemistry analysis of several deep wells in the Valley. The geothermal gradient in the Alamosa area appears to be greater than estimated by earlier studies. Temperature logging of the Alamosa Geothermal Well indicates a gradient of 2.9 degrees F per 100 feet of depth. This is equivalent to about 47 degrees C per kilometer of depth, Extrapolation indicates an expected temperature of 340 to 350 degrees F at a depth of 10,000 feet in the Alamosa area. This is considered to be well within the range of temperature gradients expected for an active rift zone. Though it is likely that there will be local areas of lower gradient within the Valley, the iv