Five aquifers in crystalline rocks of Archean and Proterozoic age in Minnesota include in descending order the North Shore Volcanic, Sioux Quartzite, Proterozoic metasedimentary, Biwabik Iron formation and undifferentiated Precambrian aquifers. The North Shore Volcanic aquifer generally yields < 15 gal/min to wells from interflow sediments and fractures in the basaltic lava flows along the northern shore of Lake Superior and along the upper St. Croix River. Dissolved solids concentrations range from 91 to 74,300 mg/L, and the water is of several chemical types. The Sioux Quartzite aquifer yields from 1 to 450 gal/min to wells open to joints and fractures and loose sand zones in the predominantly pink orthoquartzite in southwestern Minnesota. Dissolved solids concentrations range from 237 mg/L in water from wells in outcrop areas to 2,300 mg/L from wells where the Sioux Quartzite aquifer underlies Cretaceous rocks or thick Des Moines drift. The water generally is a calcium sulfate type. The Proterozoic metasedimentary aquifer generally yields < 20 gal/min to wells in weathered regolith and fractures in thin-bedded gray to black argillite in north-central Minnesota. Dissolved solids concentrations generally range from 126 to 340 mg/L, and the water is a calcium magnesium bicarbonate type. The Biwabik Iron formation aquifer yields 1,000 gal/min to wells in leached zones in the ferruginous chert and interbedded hematite and magnitite iron ore in north-central Minnesota. Dissolved solids range from 157 to 388 mg/L in water that is a calcium magnesium bicarbonate type. The undifferentiated Precambrian aquifer generally yields < 25 gal/min to wells from fractures and the weathered regolith developed on a variety of crystalline-rock types. Wells have been developed in parts of the aquifer throughout the State except in the southeast where it is too deeply buried. Dissolved solids concentrations average < 400 mg/L in central and northeastern Minnesota, but average about 700 mg/L in the northwest and 900 mg/L in the south west. The water is a calcium magnesium bicarbonate type in central and northeastern Minnesota and a variety of mixed water types in northwestern and Southwestern Minnesota.