The C-aquifer's main water-bearing units are the Kaibab Limestone, Coconino Sandstone and upper sequences of the Supai Formation. The C-aquifer is the largest aquifer in the Little Colorado River Plateau basin with an areal extent of 21,655 square miles (Figure 9). The aquifer is generally utilized, however, only south of the Little Colorado River and along the eastern edge of the basin by communities such as Flagstaff, Heber, Overgaard, Show Low, Snowflake, and Concho. North of the river, the C-aquifer is either too deep to be economically useful or the water quality is unsuitable for most uses because of the high content of dissolved salts. North of the Little Colorado River, total dissolved solids concentrations in the C-aquifer range from 1,000 to 64,100 milligrams per liter (Mann and Nemecek, 1983).

The C-aquifer is recharged by rainfall and by runoff from the San Francisco Plateau, Mogollon Rim, White Mountains, and Defiance Uplift. Recharge to the C-aquifer along the Mogollon Rim and White Mountains is estimated to be over 500,000 acre-feet per year (Arizona Department of Water Resources, 1988). Groundwater in the C-Aquifer moves to the northwest from the large areas of inflow on the south and east (Mann and Nemecek, 1983).

Aquifers of the Little Colorado River Plateau basin contain large quantities of groundwater in storage, however, they are in a sensitive relationship with the Little Colorado River and its perennial tributaries. Lowering of hydrostatic heads by excessive groundwater withdrawals may cause some perennial reaches of the streams to dry up (Mann, 1976).

The C-aquifer is the source of water for Sterling Spring at the head of Oak Creek in the Verde River basin. Future development of this aquifer and the limestone aquifer in the Flagstaff area should be preceded by an area-wide hdyrologic study. Local heavy withdrawals from the C-aquifer may also cause upward shifting of the salt water interface from the evaporites in the Supai Formation near Joseph City (Mann and Nemecek, 1983).

The D- and C- regional aquifers are still in hydrostatic equilibrium (steady-state); however, local groundwater sinks or cones of depression are developing in areas of heavy pumpage (Arizona Department of Water Resources, 1991) such as the paper mill near Snowflake and three of the power plants: Springerville Generating Station, Coronado Generating Station (St. Johns), and Cholla Generating Station (Joseph City/Holbrook). The Navajo Generating Station, near Page, uses surface water from Lake Powell. Water levels in wells that tap the confined area of the N- aquifer are declining because of heavy withdrawals for the Black Mesa coal mine slurry pipeline.