The Clarion River and Redbank Creek basin occupy 1,280 and 545 square miles, respectively, in northwatern Pennsylvania. The area is mostly in Clerion, Elk, and Jefferson Counties and is approximately 70 miles long and 30 miles wide. All drainage is to the Allegheny River. Sedimentary rocks of Late Devionian Early Mississippian, and Pennsylvanian age underlie the area. Rocks of Late Devonian age underlie the entire area and crop out in the deep stream valleys in the north. Lower Mississippian rocks generally crop out in strips along major stream valleys; the strips are narrow in the south and broaden northward. Pennsylvanian rocks cover most of the interfluvial areas between major streams. The Upper Devonian and Lower Mississippian rocks are composed mostly of alternating sandstone and shale. Sandstone may intertongue laterally with shale. The Pennsylvanian rocks are most heterogeneous and contain many commercial coal beds. The major mineral resources are bituminous coal, petroleum, and natural gas. Narly all coal production is from strip mining in Clarion, Elk, and Jefferson Counties. Total coal production exceeded 8 million short tons in 1976. The basins are south and east of the major oil-producing regions in Pennsylvania, but more than 50,000 barrels of crude oil were produced here in 1975. Commercial quantities of natural gas are also obtained. Thirty-three public water-supply systems furnish about two-thirds of the water for domestic use. Surface water is the source of about 90 percent of public-supply water. The remainder is from wells and springs. In an average year, 64 percent of the precipitation in the Clarion River basin and 60 percent in the Redbank Creek basin leave the area as streamflow. The percentage of annuual discharge from each basin that is base runoff averaged 53 and 51 percent, respectively, during 1972-75. Only 4 of 10 stream-gaging stations recorded an average 10-year, 7-consecutive day low flow of at least 0.15 cubic feet per second per square mile. Most wells are completed on bedrock. Yields of bedrock wells are affected mostly by rock type, type of overburden, topography, depth of water-bearing zones, and by the rate and duration of pumping. Water in the bedrock occurs chiefly along fractures and bedding planes. Most wells get water from several zones. Yielding zones occur less frequently as depth increases, but are reported as much as 400 feet below land surface. Optimum well depth is about 350 feet. Well yields range from less than 1 to more than 550 gallons per minute. The best bedrock aquifers are the Lower Mississippian rocks, which have a median specific capacity of 4.3 gallons per minute per foot of drawdown compared to median between 0.38 and 0.67 in the Conemaugh, Allegheny, and Pottsville Groups. The major water-qualitty problems are due to high concentrations of iron, manganese, hardness, and acidity. Some of these problems are related to coal mining that has degraded water quality in parts of Clarion, Clearfield, Elk, and Jefferson Counties. Water-quality problems result from the rock composition. Many streams have low alkalinity concentrations and, consequently, have little capacity to neutralize the acid water from coal mines. Large forested areas, with little development, in Elk, Forest, and Jefferson Counties, have good quality water. The water from over three-quarters of the bedrock wells sampled has dissolved-solids concentratins less than 250 milligrams per liter. Water from aqufers of Pennsylvanian age is generally lower in dissolved solids than that from Lower Mississippian aquifers. Salt water is not a problem, except locally in Devonian rocks. Water from wells on hilltops is generally of better quality than that from wells in valleys (median dissolved solids 140 versus 340 millgrams per liter). In many valleys in Clarion and Jefferson Counties, old abandoned flowing oil and gas wells contribute high