The Quaternary Gravel is mostly poorly sorted, fine- to coarse-grained gravel that is cemented by caliche (calcium carbonate formed by the evaporation of water).

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.