The effects of the recent drought 1942-56 have varied widely in the Southwestern basins of interior drainage which include, in addition to the Great Basin of Nevada, Utah, and California many smaller basins in Texas, New Mexico, and Arizona. These closed basins are characteristically separate hydrologic units, and their water resources may logically be developed and regulated independently, which is not true of the subdivisions of the Rio Grande and Colorado River basin. Several topographically closed basins are independent hydrologic units with respect to surface water but are interconnected by ground-water circulation.