This report is a compilation of well construction data, lithologic and geophysical logs, and water level and water quality data for selected wells and springs in the South Branch Casselman River and Marsh Run drainage basins, Garrett and Washington Counties, Maryland. The report contains, for the two areas combined, records of 202 wells and 57 springs; periodic water level measurements and field determinations of specific conductance, pH, and water temperature for 33 wells and 7 springs; geophysical logs for 1 well and lithologic logs for 113 wells; and multi-year water-level data for 9 observation wells. (USGS)