Hydrologic data were collected from 36 wells and 80 springs in the San Miguel River basin from 1977 to 1979. Depth to water was measured for 22 wells and discharges were measured for 53 springs. Chemical analyses for water samples collected from 23 wells and 25 springs indicated larger dissolved solids concentrations in bedrock water samples than in alluvial water samples. Drillers ' records obtained from the Colorado State Engineer 's Office for 86 wells indicate generally larger yields from wells completed in alluvium than in bedrock. (USGS)