Pinal MODFLOW model development began in the late 1980's. Previous to the late 1980's, no numeric groundwater models within the Pinal AMA had been developed. Thomas Anderson (1968) developed an electric analog model simulating the groundwater depletion of Central Arizona between 1923 and 1964. Since the first ADWR Pinal MODFLOW release in 1990 the model has not been updated. The challenge in developing a model within the Pinal AMA is lack of measured data. The original ADWR MODFLOW model relied on data provided through a report by Hardt and Cattany entitled "Basic Groundwater Data for Western Pinal County"(1964).
In October 2007 the Pinal AMA MODFLOW model began the initial phase of update that included both the steady state (circa 1900) and the transient model (1922-2009). The Pinal model geology update was completed in 2010 and the updated modeling report that includes the simulation of subsidence was completed in 2014.