As of 1999, surface water collected and stored in reservoirs is the sole source of municipal water for the city of Williams . During 1996 and 1999, reservoirs reached historically low levels. Understanding the ground-water flow system is critical to managing the ground-water resources in this part of the Coconino Plateau. The nearly 1,000-meter-deep regional aquifer in the Redwall and Muav Limestones, however, makes studying or utilizing the resource difficult. Near-vertical faults and complex geologic structures control the ground-water flow system on the southwest side of the Kaibab Uplift near Williams, Arizona. To address the hydrogeologic complexities in the study area, a suite of techniques, which included aeromagnetic, gravity, square-array resistivity, and audiomagnetotelluric surveys, were applied as part of a regional study near Bill Williams Mountain.

The primary objectives of the Atlas are to present an overview of water supply and demand conditions [as has not been available on a statewide basis for over ten years], to provide water resource information for planning and resource development purposes and to help identify the needs of communities throughout Arizona, particularly those outside the AMAs [the five active management areas].

This report characterizes the relationship of geology to groundwater occurrence and flow, with emphasis on determining the thickness of the valley-fill aquifer and water yielding properties of the fractured rock aquifers. Develops a water budget for the drainage basin and classifies the groundwater quality and identifies the likely sources of nitrate in groundwater.