The steady-state groundwater system in Mesozoic rocks in the Four Corners area, Utah, Colorado, Arizona, and New Mexico, was simulated with a finite-difference digital-computer model to improve the understanding of the system. The simulated area is 4 ,100 sq mi, and it includes three aquifers. The Entrada-Navajo aquifer includes the Wingate, Navajo, and Entrada Sandstones. The Morrison aquifer includes the sandstone units of the Morrison Formation. The Dakota aquifer includes the Burro Canyon Formation and Dakota Sandstone. The simulation of the groundwater system had a mean error (error is absolute value of residual) of 70 ft for the Entrada-Navajo aquifer, 67 ft for the Morrison aquifer and 79 ft for the Dakota aquifer. The hydraulic conductivity used in the simulation ranged from 0.38 to 0.47 ft/day. Simulated inflow to the groundwater system was 30,000 acre-ft/yr. 48% of the inflow is from infiltration of precipitation within the simulated area, and 42% is from infiltration in 145 sq mi of mountain areas adjacent to the simulated area. Simulations indicated that some vertical inflow of water is needed between the Entrada-Navajo and Morrison aquifers to develop a reasonable representation of the system.
