Reconnaissance of ground-water resources in the North Fork Gunnison River basin, southwestern Colorado

Aquifers of large areal extent in the North Fork Gunnison River basin are found in the alluvium and bedrock. Alluvial aquifers yielded water with dissolved solids concentrations ranging from 43 to 2,300 mg/L. Dissolved solids concentrations of water samples from the Mesaverde Formation of Late Cretaceous age and the Dakota Sandstone and Burro Canyon Formations of Late and Early Cretaceous age ranged from 56 to 3,200 mg/L. Dissolved solids concentrations of water samples from Mancos Shale ranged from 1,800 to 8,200 mg/L. Most wells in the North Fork Gunnison River basin are at altitudes below 7,500 ft, yield from 2 to 40 gal/min and are completed in alluvial sand and gravel, sandstone , or fractured bedrock. Springs generally are at altitudes above 7,000 ft, discharge from perched water tables at geologic contacts, have calcium magnesium bicarbonate water types, and are much less saline than water from wells. (Author 's abstract)