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The ground -water system in the Twin Cities area contains five aquifers (Guswa and others, 1982, table 1). Two of these aquifers, the Prairie du Chien -Jordan and Mount Simon -Hinckley, supply about and 10 percent, respec- tively, of the ground -water pumped in the 3,000 mi seven -county area (fig. 1). 7his report describes water levels and water -level changes in these aquifers in the Twin Cities during the period 1971-80. State and local agencies, industries, and municipalities need information on water levels and water -level changes caused by pumping to anticipate the effects of increased pumping on the aquifers. For example, ground -water with- drawals have caused water -level declines of about 200 ft in the Mount Simon - Hinckley aquifer and 90 ft in the Prairie du Chien -Jordan aquifer since 1885 (Reeder, 1966; Norvitch and others, 1973, p. 118). In addition, water, levels decline sharply during summer as pumping increases and recover during winter as pumping decreases. To provide the needed water -level data, the U.S. Geological Survey, in cooperation with the Metropolitan Council of the 'twin Cities and the Minnesota Department of Natural Resources, measured water levels in wells throughout the Twin Cities area during winter and summer 1965, 1971, and 1980, summer 1977, and winter 1978. These water -level data will also be used to calibrate a digital ground -water -flow model of the Twin Cities area (Guswa and others, 1982). This report documents water -level data collee--d during winter and summer 1980 for the Prairie du Chien -Jordan and Mount Simon -Hinckley aquifers and compares the data with those collected during winter 1971. Specific objectives are to (1) compare short-term and long-term changes in water levels in the two aquifers, (2) examine the effects of major pumping centers on water levels over the 1971-80 period, and (3) describe ground -water -flow patterns in the two aquifers. This report contains a trief description of the hydrologic setting, a description of the water -level observation network and methods used to col- lect data, water -level mapb for winter 1971 and winter and summer 1980 for both aquifers, seasonal and long-term water -level -change maps, and hydrographs of selected wells. Water -level data for 1971 and 1980 were analyzed in detail because this was the calibration period chosen for the ground -water -flow model. In 1966, the U.S. Geological Survey released 14 maps depicting histor :al water levels and water -level changes for the Prairie du Chien -Jordan and Mount Simon -Hinckley aquifers in Uie Minneapolis -St. Paul Metropolitan Area Reeder, 1966). The maps show water levels for both aquifers for 1885, 1949, 1959, and 1%5 and changes in water levels from 1885 to each of the subsequent years. Norvitch and others (1973) provide water -level maps for both aquifers for winter 1970-71 and for the Prairie du Chien -Jordan for August 1971, and water - level -change maps for the Prairie du Chien -Jordan for December 1970 to August 1971 and winter 1%5 to winter 1970-71. Hult and Schoenberg (1981) p ovide more detailed water -level data for both aquifers for 1979 in a 110-mi area surrounding St. Louis Park, a western suburb of Minneapolis. In addition, a