The basins of Maggie, Marys, and Susie Creeks in northeastern Nevada are along the Carline trend, an area of large, low-grade gold deposits. Pumping of ground water, mostly for pit dewatering at one of the mines, will reach maximum rates of about 70,000 acre-ft/yr (acre-feet per year) around the year 2000. This pumping is expected to affect ground-water levels, streamflow, and possibly the flow of Carlin spring, which is the water supply for the town of Carlin, Nev. Ground water in the upper Maggie Creek Basin moves from recharge areas in mountain ranges toward the basin axis and discharges as evapotranspiration and as inflow to the stream channel. Ground water in the lower Maggie, Marys, and Susie Creek Basins moves southward from recharge areas in mountain ranges and along the channel of lower Maggie Creek to the discharge area along the Humboldt River. Ground-water underflow between basins is through permeable bedrock of Schroeder Mountain from the upper Maggie Creek Basin to the lower Maggie Creek Basin and through permeable volcanic rocks from lower Maggie Creek to Carlin spring in the Marys Creek Basin. The only source of water to the combined area of the three basins is an estimated 420,000 acre-ft/yr of precipitation. Water leaves as runoff (38,000 acre-ft/yr) and evapotranspiration of soil moisture and ground water (380,000 acre-ft/yr). A small part of annual precipitation (about 25,000 acre-ft/yr) infiltrates the soil zone and becomes ground-water recharge. This ground water eventually is discharged as evapotranspiration (11,000 acre-ft/yr) and as inflow to the Humboldt River channel and nearby springflow (7,000 acre-ft/yr). Total discharge is estimated to be 18,000 acre-ft/yr.