The Mesozoic-Paleozoic Rocks of the Beaver Creek Watershed
comprise rocks from the latest Permian and early Triassic
Periods of the Geologic
Time Scale. Though these formations are above the regional aquifer, they are important transmitters of water to lower aquifer units. The three Mesozoic-Paleozoic units are, from youngest to oldest:
Triassic Moenkopi Formation (~ 248 to 230 m.y.): The Moenkopi is separated from the
Kaibab by an unconformity, indicating that erosion took
place prior to deposition of the Moenkopi. This formation
consists of claystone and mudstone in the upper part,
along with some gypsum, indicating that evaporation was
taking place at the time of deposition. The unit
also contains siltstone, sandstone, and conglomerate. The
siltstone and mudstone of this formation sometimes act
as barriers to groundwater flow, creating locally perched
aquifers. These relatively impermeable layers can also inhibit downward movement of water into lower aquifer units.
Permian Kaibab Formation (~ 260 m.y.): A massive, fossiliferous limestone and dolomite unit that is directly overlain in many places by Tertiary volcanics in the Beaver Creek Watershed. The Kaibab is fairly porous and permeable as a result of fairly dense fracturing throughout the unit, allowing water to transmit to lower aquifer units.
Permian Toroweap Formation (~ 262 million years old): The lower part is a massive sandstone with horizontal bedding and some cross-beds. This grades upward into layers of siltstone and mudstone that alternate with sandstone. Because the Toroweap and Coconino Sandstone units are indistinguishable within Wet Beaver Canyon, Thompson (1968) chose to refer to all cross-bedded sandstones within the canyon as Coconino Sandstone. The Toroweap is among the water-transmitting units of the Beaver Creek Watershed and surrounding watersheds.
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.
