The Humboldt River Basin encompasses an area of nearly 17,000 mi2 in north-central Nevada; it is the only major river basin that begins and ends entirely within the State (fig. 1). The study area for this report is the middle Humboldt River Basin, which consists of 14 hydrographic areas that encompass 7,400 mi2 (fig. 1 and table 1). The principal tributaries to the Humboldt River in the study area are Pine Creek, Rock Creek, and Reese River.