Description:
This report presents a selected bibliography of water quality studies covering the upper
Gila River watershed and discusses a few ofthe more important publications. Previously
unpublished water quality data are reported for the Gila River and groundwater in the Safford
basin. References cover the Gila River watershed between the Arizona-New Mexico border on the
east and Coolidge Dam on the San Carlos Indian Reservation on the west. The watershed includes
roughly 11,470 square miles, about half in Arizona and half in New Mexico.
The Gila River enters Arizona near the town of Duncan and flows to the northwest through
the Duncan basin, then cuts across the northern Peloncillo Mountains to enter the middle of the
Safford-San Simon Valley east of Safford. After flowing northwest to the north end of the Safford
basin the river turns southwest, exiting the basin through a bedrock gorge cut at right angles to the
Mescal and Dripping Spring Mountains.
The geologic history of the upper Gila region controls the hydrology and the chemistry of
surface water and groundwater in the watershed. Both the Duncan and Safford basins are deep,
sediment-filled structural troughs containing abundant lacustrine (lake) and playa sediments,
reflecting long periods of closed-basin conditions (Harris, 1997). Soluble minerals such as halite,
carbonates, gypsum, and anhydrite are common in the basin-fill sediments and contribute
significant TDS to the groundwater of the basins and to the Gila River (Harris, 1999).
( 67 pages)