The units of the early Paleozoic Era comprise rocks from the Cambrian, Devonian, and Mississippian Periods of the Geologic Time Scale. Each of these formations is part of the regional aquifer in at least a limited way. Their extent within the Beaver Creek watershed is limited to a small outcrop in the western portion. The formations vary in composition and include, from youngest to oldest::

MIssissippian Redwall Limestone (~ 340 million years old): The Redwall is a coarse-grained, massive limestone unit that contains fractures and joints and parting along bedding planes, facilitating the transmission of water.  In some places, the Redwall was once part of the regional aquifer, but it is now above the water table and drained of water.

Devonian Martin Formation (~380 m.y.): The Martin Formation consists of fine- to coarse-grained dolomitic limestone, with minor lenses of shale and sandstone near its base and mudstone and siltstone in the upper part. The unit is part of the regional aquifer in places.

Cambrian Tapeats Sandstone (~ 520 m.y.): The Tapeats is a medium- to very coarse-grained cross-bedded sandstone unit with lenses of conglomerate and upper layers of mudstone and siltstone.  The unit is likely part of the regional aquifer in many places, though its depth is great enough that no known wells penetrate it.

 

Reference:

Owen-Joyce, S.J. and Bell, C.K., 1983 Appraisal of Water Resources in the Upper Verde River Area, Yavapai County, Arizona, Arizona Department of Water Resources Bulletin 2 (Prepared by the U.S. Geological Survey), available online at: http://www.verde.org/usgs/usgsstud.html.