Consideration of land-management alternatives in parts of the Fort McDermitt Indian Reservation has prompted an evaluation of water resources in the reservation and vicinity. The study area comprises (1) about 9 square miles of reservation land, plus adjacent areas, on and bordering the floor of Quinn River valley near McDermitt, Nev., and (2) the uninhabited 5.6-square-mile Hog John Ranch (also part of the reservation) and adjacent areas along the boundary between Kings River and Desert Valley, about 35 miles southwest of McDermitt. In both areas, the valley-fill reservoir forms the principal source of ground water. The reservoir is at least 1,225 feet deep at one site near McDermitt. Volcanic rocks also form an important source of ground water for several wells near McDermitt. A 12-inch diameter, 720-foot test well drilled on the reservation near McDermitt produced 360 gallons per minute with a drawdown of 149 feet (specific capacity, 2.4 gallons per minute per foot of drawdown). A transmissivity of 640 feet squared per day for this well was obtained from a 44-hour pumping test. Transmissivities for 6 Other wells in the McDermitt area ranged from 710 to 11,000 feet squared per day. In this area, water levels ranging from 3 to 250 feet below land surface have remained almost the same as those of 1964. Depth to water generally increases away from the valley lowlands. The valley-fill reservoir in the Hog John Ranch area is at least 350 feet deep. Depth to water in the vicinity of the Ranch ranges from 0.25 to 48 feet, with deeper water levels generally found at higher land elevations. Net change in these water levels has been negligible for a period of nearly 30 years. Two adjacent test wells at the Ranch were augered to depths of 33 and 90 feet during this study, and completed with well-bottom screens. Differing water levels in the two wells indicate a minimum upward hydraulic gradient of about 0.07 foot per foot in the zone penetrated by the holes. Water quality in the McDermitt area is generally suitable for most uses. In the Ranch area, water salinity appears to decrease with increasing well depth, and is generally suitable for irrigation at depths exceeding 50 feet. The East Fork Quinn River, which flows directly through the inhabited part of the reservation, has an average runoff of about 20,000 acre-feet per year at the gage 7 miles east of McDermitt. Streamflow from Quinn River, Kings River, and Desert Valleys passes intermittently through the Ranch by way of the Quinn River, but the quantity of flow is not known.