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I H? en I CD C\l (=, 0 I I I I I I I I I I I I I I I I I faulted rift zones are expected, with good confidence, to show temperature gradients in that range, Thermal waters in the Valley appear to occur preferentially along two lines: one north-south through Villa Grove and the San Luis Hills, and the other east-west through the Summer Coon volcanic ared, There is evidence for structure along the two lines, as seen weakly on the TM satellite imagery for the east-west line, and strongly on the TM imagery and seismic sections for the north-south line. At the locations of fault zones which allow upward leakage from great depths (deeper than HSU-3), wells and springs may show waters with unusually high concentrations of organic carbon, dissolved gasses, silica, and fluoride, as well as sodium and chloride, uranium and similar heavy metals, and certain anionic complexes stable at high pH levels. There is only limited direct evidence for this at present, at localized areas near Alamosa and Moffat. Unless more data becomes available, this conclusion will remain inferential and not definite. Where shallow waters mix with deep waters, dilution may mask the chemistry of the deeper contributions. This is expected to be the case at some distance from deep-seated, rift-related fault zones. It has been shown with good confidence that there are water quality differences with depth, and that there is upward leakage within HSU-3. The areal extent of such mixing, however, has not been well defined in the Valley. The sump area of the closed basin in the Valley lies in an area where several major, deep-seated fault zones intersect. Upwelling ground water along such faults may have contributed to the near-surface waterlogging in that area. This should be considered as a hypothesis, and not a definite conclusion, unless more data becomes available. v