The Tertiary Sedimentary Rocks (older than Tertiary Volcanics) consist of a variety of lithologies (rock types), including gravel, conglomerate, sandstone, siltstone, clay, marl, and limestone. They have not been recorded as containing clasts of the Tertiary Volcanics, so they could be interpreted as being older. There are no known absolute age dates to confirm this interpretation.

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.