The Upper San Pedro MODFLOW model development began in the early 1990's. Previous to the early 1990's, Freethey (1982) developed a 2D USGS Trescott groundwater model within the Upper San Pedro (USP) basin (Mexico to Fairbank). Freethey's model laid the conceptual framework for much of the future USP modeling effort.
In 1992 Vionet and Maddock developed a MODFLOW model of the USP followed by the 1996 release of the ADWR model and associated scenarios representative of 1940-1990. Since the 1996 ADWR model release, two additional models representative of the USP were completed (2000 & 2007). The most recent MODFLOW model for the USP was developed by the USGS Pool and Dickinson (SIR 2006-5228) (2007).