Hydrogeology of the Quitobaquito Springs area, La Abra Plain, and the Rio Sonoyta Valley, Organ Pipe Cactus National Monument, Arizona and Sonora, Mexico

A hydrogeological study was performed on the cross-boundary valley between Organ Pipe Cactus National Monument, Arizona and the Rio Sonoyta Valley, west of Sonoyta, Mexico. The study was carried out to evaluate present hydrologic conditions in the valley and to assess the impact of irrigation ground-water withdrawals in Sonora on water resources in the Monument and in particular the spring system in the Quitobaquito Hills. Through evaluation of available hydrogeologic data, three main aquifers were identified in the north half of the valley. These are the alluvial basin fill and fan system of La Abra Plain, the fractured crystalline rock system of the pediments of the Quitobaquito Hills, and the fluvial aquifer associated with the active channel of the Rio Sonoyta. A detailed evaluation of the location, discharge, and radioisotope composition of the springs in the Quitobaquito Hills was made to characterize the ground-water flow system supplying the springs and to evaluate the possible effects of irrigation withdrawals in Sonora on their discharge. (Abstract shortened by UMI.