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Earth Notes: Portrait of the Coconino Aquifer

A view of a desert landscape with a few scattered buildings, and a tall snow-capped blue peak in the distance.
City of Flagstaff
The City of Flagstaff purchased Red Gap Ranch in 2015, which comes with a supply of water from the C-aquifer, for future water development.

The most productive aquifer in northern Arizona is named after its main water-bearing rock unit - the Coconino Sandstone. The Coconino or ‘C’ aquifer underlies 27,000 square miles from the community of Parks just west of Flagstaff, across into New Mexico and southern Utah.

Major recharge occurs along the Mogollon Rim. Here the rock strata dip toward the northeast and direct snowmelt and rainwater downward. There’s also recharge along streams like Clear Creek and Chevelon Creek.

The City of Flagstaff is one of the biggest users of the C-aquifer. Water is pumped from wells that are typically around 1,200 feet deep, although new "urban wells" being developed may not reach water until 1,500 feet below ground.

Typically, south of Interstate 40, the C-aquifer delivers high-quality water. But north of the interstate and along a line west of Snowflake through Winslow, water flows through salt beds in the Schnebly Hill Formation, increasing the concentration of sodium chloride.

Winslow is located close to the boundary of that saltier water. Pumping operations there, along with future withdrawals for the Navajo Nation and Flagstaff, will be monitored carefully and wells shut off if necessary, to avoid drawing the saltier water into the municipal supplies.

The time for water to recharge in the C-aquifer varies greatly — from less than 200 years near Lake Mary to many thousands of years towards the Utah-Arizona border.

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