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<:) N ....... ~ hydrostratigraphic unit. Spring discharges, artesian well flows, and drill-stem test yields from these units commonly exceed 50 gal/min (Hampton, 1974; Hood, 1976; Sumsion, 1976; Barrett and Pearl, 1977; Galloway, 1982; Teller and Welder, 1983). Discharges of several hundred to 3,200 gal/min can occur from the Devonian and Mississippian carbonate rocks unit; discharges of 100 to 60Q gal/min can occur from the Pennsylvanian and Permian sandstone unit. Hydraulic-conductivity values for the' Devonian and Mississippian carbonate rocks unit range from less than 0.001 ft/d in basins to more than 100 ft/d in uplifted areas. Hydraulic-conductivity values for the Pennsylvanian and Permian sandstone unit range from less than 0.0001 ft/d in basins to 20 ft/d in uplifted areas. Hydraulic Conductivity and Transmissivity -- Aquifer-test data for the Devonian and Mississippian carbonate rocks hydrostratigraphic unit in northwestern Colorado were obtainable at only five sites. Additional data were obtained at two sites in Utah and Wyoming within 25 mi of the study area. Aquifer tests analyzed to determine hydraulic conductivity included five drill-stem tests, one pumping test, and the two flowing-well tests at Glenwood Springs that were discussed previ- ously. Sources of data for tests other than those at Glenwood Springs included Petroleum Information Corporation, Colorado Division of Water Resources, and ARea (written commun., 1984-85). Hydraulic conductivity was calculated from the drill-stem test data by the methods of Homer (1951) and Earlougher (1977), and by a method described in Supplement B in the "Supplemental Informa- tion" section at the back of this report. Hydraulic conductivity was calculated from the pumping test data by the method of Lohman (1979, p. 52). Hydraulic-conductivity values calculated from the analyzed test data increase from structural basins to uplifted areas. Hydraulic-conductivity values indicated by drill-stem tests in the Uinta, Piceance, and Sand Wash basins range from 0.00057 to 0.0097 ft/d. In contrast, hydraulic-conductiv- ity values indicated by two drill-stem tests and a pumping test on the flanks of the Sawatch Range, Park Range, and Uinta Mountains range from 0.49 to 0.9- ft/d. Hydraulic conductivity on the in- tensely faulted south-western flank of the White River Plateau at Glenwood Springs is at least 170 ft/ d. The available data, though limited, indicate that hydraulic-conductivity values in the center of uplifted areas are at least three orders of magnitude larger than in the center of adjacent basins. Transmissivity, like hydraulic conductivity, also is larger in uplifted areas than in structural basins (see Fig. 4 in main text, copied from Geldon). Transmissivity values in the study area were obtained directly from aquifer tests only at Glenwood Springs and near Aspen. Elsewhere in the study area, transmissivity was calculated from the product of hydrostratigraphic unit thickness and measured or estimated hydraulic conductivity at grid centers on a lO-mi by lO-mi grid. This analysis indicates that transmissivity in the hydrostratigraphic unit ranges from less than 0.1 to 10 ft**fd in structural basins and from 10 to more than 1,000 sq ft/d in uplifted areas. The transmissivity in the vicinity of Glenwood Springs, as indi- cated by the first and second Redstone well tests, is 47,000 sq ft/d. than 1,000 sq ft/d in uplifted areas. The transmissivity in the vicinity of Glenwood Springs, as indicated by the first and second Redstone well tests, is 47,000 sq ft/d. Hydrodynamics A composite-potentiometric surface map was prepared from all available potentiometric head and spring-altitude data in northwestern Colorado (Fig. 5 in main text, copied from Geldon). This map indicates that water in the Devonian and Mississippian carbonate rocks hydrostratigraphic unit generally flows toward structural basins and river valleys from topo- graphically and structurally high areas on the east and south and in the center of the study area. A major ground-water divide extends between the Uinta Mountains on the west and the Park Range on the east. South and east of Glenwood Springs, water in the Devonian and Mississippian carbonate rocks hydrostratigraphic unit generally flows northwestward, from recharge areas in the Sawatch Range, White River Plateau, and Elk Mountains to the Colorado River. Recharge occurs from pre- A-S