Sandra J. Owen-Joyce and C. K. Bell

The part of the upper Verde River area in the Plateau uplands province is underlain by a sequence of almost flat-lying sedimentary rock units overlain in places by volcanic rocks and alluvium (pl. 1). The oldest Paleozoic rock unit exposed in this part of the study area is the Redwall Limestone, which is along the Oak Creek fault (Levings, 1980). Several oil- and gas-test holes and a few water wells indicate the Redwall Limestone is underlain by the Martin Formation, Tapeats Sandstone, and Precambrian granitic rocks. Rock units that overlie the Redwall Limestone are the Supai Formation, Coconino Sandstone, Toroweap Formation, and Kaibab Limestone. The Naco Formation crops out along Fossil Creek, which is the northwest limit of its deposition, where it interfingers with the Supai Formation. The Moenkopi Formation crops out near the Mormon Mountain anticline, near the northeast boundary of the area, and along Sycamore Canyon. Tertiary rocks lie unconformably on older rock units. The Tertiary rocks include the Hickey Formation, Perkinsville Formation, intermediate basalt west of Black Mountain (Lehner, 1958), unnamed volcanic rocks and associated sediments in the northwest corner of the area (Krieger, 1965; 1967a, b), and the Tertiary basalts of Moore and others (1960) and Twenter and Metzger (1963) in the north and east parts of the area. Alluvium occurs locally along stream channels.

In the Black Hills, volcanic rocks overlie metamorphic, granitic, and flat-lying sedimentary rocks, which locally are tilted by faulting. The Black Hills contain the only outcrops of Precambrian rocks in the area (pl. 1). Paleozoic sedimentary rocks lie unconformably on the Precambrian rock units and include the Tapeats Sandstone, Martin Formation, Redwall Limestone, and Supai Formation. Tertiary rocks lie unconformably on the Paleozoic rocks and include the basalt flows and sediments of the Hickey Formation, Perkinsville Formation, and unnamed sedimentary and volcanic rocks (Krieger, 1965; 1967a, b).

The Verde Valley is underlain by rock units of Tertiary and Quaternary age. The Verde Formation, which covers about 325 mi2 of the valley, is a deposit of mudstone, limestone, and sandstone that contains interbedded volcanic rocks that are exposed along the east and south margins of the valley. Wells drilled near the boundaries of the Verde Formation penetrate the surrounding flat-lying sedimentary rocks found below the Mogollon Rim and in the Black Hills. The deepest hole, which was drilled in the south-central part of the valley, was 1,625 ft deep and bottomed in 225 ft of basalt flows. What underlies the basalts is unknown. Alluvium occurs along the channels and flood plains of major streams. Gravel overlies the Verde Formation between the Black Hills and the Verde River.

Description of the Water-Bearing Rock Units

For the purpose of this report, the rock units that are of interest are those from which water can be obtained. The following summaries describe the rock units from oldest to youngest. The complete stratigraphy and more detailed lithologic descriptions appear on plate 1.

The rocks of Precambrian age include 20,000 feet of metamorphosed volcanic and tuffaceous sedimentary rocks (Anderson and Creasey, 1958, p. 9), which are intruded by granitic to dioritic rocks. The Precambrian rocks are faulted and fractured.

The Tapeats Sandstone of Cambrian age unconformably overlies the Precambrian rock units and ranges in thickness from 0 to 150 ft. The lower part is a medium-grained to very coarse grained crossbedded sandstone with lenses of conglomerate cemented by silica and iron oxide. Where siliceous cement is dominant, the rock unit is hard, almost a quartzite. The lower part grades upward into a shaly siltstone and limy or dolomitic mudstone that are moderately cemented with siliceous and calcareous cement.

The Tapeats Sandstone and the overlying Martin Formation of Devonian age appear to be in gradational contact. The 500 ft of Martin is mainly a dolomitic limestone, although locally at the base is lenticular sandstone. The dolomitic limestone is fine to coarse grained. The lower part of the unit contains interbeds of shale and a silica cemented sandstone bed, which ranges in thickness from 1 to 3 ft. The uppermost part contains shaly mudstone and platy siltstone.

The Redwall Limestone of Mississippian age unconformably overlies the Martin Formation and contains 35 ft of reworked Martin at its base. The Redwall is mainly a massive, coarse-grained, and crystalline limestone, which ranges in thickness from 0 to 300 ft. Beds differ in thickness from thin bedded in the lower one-third to thick bedded in the upper two-thirds. Some beds within the Redwall Limestone are highly fractured and contain solution channels and caverns formed along joints or bedding planes, or at random.

The Redwall Limestone is overlain primarily by the Supai Formation of Pennsylvanian and Permian age except in the extreme southeastern part of the study area along Fossil Creek where it is unconformably overlain by the only outcrop of Naco Formation of Pennsylvanian age seen in the area. The Naco Formation is 475 ft thick and interfingers with the Supai Formation. The Naco Formation is a limy siltstone and fine-grained sandstone with a few interbeds of limestone and at the base is a layer of sandy shale and chert breccia.

The Supai Formation was laid down on a karst-type erosion surface of the Redwall Limestone. Lenticular beds of a basal conglomerate contain pebbles derived from the Redwall Limestone. The Supai is divided into three members (Huddle and Dobrovolny, 1945). The lower member, which is 1,100 ft thick, contains alternating beds of sandstone, siltstone, and some limestone in the upper part and siltstone with some shaly mudstone and a few beds of limestone conglomerate, limestone, and sandstone in the lower part. At the base is a chert breccia or limestone conglomerate. The middle member, which is 300 ft thick, contains alternating beds of siltstone, mudstone, and sandstone and at the base a limestone bed. In the upper section of the member, lenticular beds of dolomitic intraformational conglomerate contain well-rounded limestone pebbles in a siltstone matrix. Some siltstone beds are calcareous. The dolomitic and calcareous beds are subject to solution as indicated by sinkholes in the Sedona area. The upper member, which is 625 ft thick, is a sequence of very fine to coarse-grained sandstone beds and a few interbedded siltstone beds. The sandstone is friable, some is calcareous, and the beds are thick and massive. Near Sedona, a sandy limestone bed 10 to 15 ft thick can be seen. The bed thins and pinches out to the west.

The contact between the Supai Formation and the Coconino Sandstone of Permian age is gradational. A transition zone, which is about 50 to 150 ft thick, is light-colored crossbedded sandstone similar to the Coconino, alternating with dark-colored siltstone similar to the Supai. The contact has been placed arbitrarily at the top of the uppermost horizontally bedded siltstone layer in order that the Coconino contains no siltstone beds.

The Coconino Sandstone is a very fine grained to fine-grained massive sandstone unit. The degree of cementation varies, but generally the Coconino is well cemented by silica, although some calcium carbonate also is present as cement. This unit is 650 ft thick and is characterized by large-scale crossbeds that are as much as 50 ft long. In some areas, the unit exhibits jointing or fracturing and parting along the planes of the crossbeds.

The Toroweap Formation of Permian age, which is as much as 350 ft thick, conformably overlies the Coconino Sandstone. The Toroweap has horizontal bedding and smaller crossbeds than the Coconino. The lower part is a massive fine-grained to coarse-grained sandstone. Some beds are calcareous and others clayey. The upper part contains alternating layers of friable and soft sandstone, siltstone, and some shaly mudstone that grade eastward to noncalcareous sandstone.

The Kaibab Limestone of Permian age unconformably overlies the Toroweap Formation. It is a limestone or dolomitic limestone. To the northwest, some beds are fine-grained massive calcareous sandstone and are somewhat friable. The unit, which is about 400 ft thick, is fractured and contains solution fissures and caverns.

An unconformity separates the Moenkopi Formation of Triassic age from the underlying Kaibab Limestone. The Moenkopi ranges in thickness from 0 to 400 ft and consists of siltstone, mudstone, claystone, and sandstone with a conglomerate at the base. The mudstone and claystone in the upper part contain stringers of gypsum.

The volcanic rocks of Tertiary age vary in thickness and are mainly basalt and andesite flows, basaltic dikes, cinder cones, and sedimentary rocks composed of volcanic material. The rocks are distributed irregularly over the study area and unconformably overlie rocks that range in age from Precambrian to Tertiary (pl. 1). The flows are characteristically faulted and jointed and locally contain layers of clay and weathered ash. The coarser interbedded sedimentary rocks exhibit more porosity than the clay and weathered ash.

The Verde Formation of Tertiary age consists of sediment that was deposited in a lake. Its thickness ranges from 0 to at least 1,800 ft (Twenter and Metzger, 1963, p. 55), but the maximum thickness is unknown. The lithology of the beds varies, and most beds are lenticular. Six facies are assigned to the formation (Twenter and Metzger, 1963): the thick limestone facies; upper, middle, and lower limestone facies; the mudstone facies; and the sandstone facies. The thick limestone facies is found in the central part of the Verde Valley and is composed of limestone and marl. The limestone is soft, marly, and chalk-like when fresh but becomes hard and resistant when weathered. Beds range in thickness from 6 in. to 5 ft. This facies intertongues with all the other facies (Twenter and Metzger, 1963, p. 50). The upper, middle, and lower limestone facies, which are mainly limestone and marl, are similar except for their position in the section. Beds are 1 to 10 ft thick and contain solution channels. The upper limestone facies is porous owing to hollow calcified plant stems. The upper, middle, and lower limestone facies radiate out from the central thick limestone facies. The mudstone facies consists of mudstone and claystone but becomes sandy and silty in places. Beds are less than 1 in. to 5 ft thick. In the southwestern part of the valley, the mudstone facies contains evaporate minerals and south of Wingfield Mesa is interbedded with tuffaceous sedimentary rocks, conglomerate, volcanic ash, and clay. The mudstone facies is reported to intertongue with the lower and middle limestone facies, whereas the sandstone facies intertongues with the middle and upper limestone facies. The sandstone facies consists of very fine to fine-grained sandstone and siltstone composed mainly of quartz and interbedded with some mudstone, claystone, and limestone. Along the margin of the valley, the sandstone facies is mainly conglomerate. The limestone beds of the formation are jointed and contain solution channels. The sandstones are friable, and the mudstones contain salt and gypsum deposits.

The Quaternary alluvium comprises channel, flood-plain, and terrace deposits found near the stream channels. The channel and flood-plain deposits are poorly sorted gravel, sand, silt, and clay, and the terrace deposits are finely stratified clay, silt, sand, and gravel. The alluvium along the streams ranges in thickness from a few feet to about 50 ft.

In the area around Munds Park, the alluvium is as much as 400 ft thick. The alluvium is composed of black and brown clay interbedded with cinders, volcanic gravel, and volcanic ash.

Structure

Structural features bound the east and west sides of the upper Verde River area. The Mormon Mountain anticline (pl. 1), which is the northeastern ground-water divide, is asymmetrical, and the southwestern limb dips toward the Verde Valley. No dips greater than 4o have been measured except where associated with a fault. The Black Hills on the west were uplifted along northwestward-trending normal faults, and the rock units dip gently toward the basin. Tertiary and Quaternary rock units in the Verde Valley are nearly horizontal or dip less than 5o except near faults where dips may exceed 5o. Faulting in this region has been described by Mears (1948, 1950), Twenter and Metzger (1963), Thompson (1968), and Levings (1980).

The northwestward-trending Verde fault zone (pl. 1) on the eastern side of the Black Hills consists of a main Verde fault and a series of parallel and subparallel subordinate faults, most of which lie to the east of the main fault. The faults dip steeply to the northeast, and the rocks on the northeast side are displaced downward. The zone is 2 mi wide near Jerome and 6 mi wide near Tule Mesa. The Verde fault exhibits the greatest vertical displacement of any fault in the study area. The throw is believed to be greater than 2,000 ft (Anderson and Creasey, 1958, p. 80). The Verde fault and the associated Bessie fault offset the Verde Formation and older formations.

Faults that displace Paleozoic rocks are from near Jerome to northeast of Perkinsville (pl. 1). The Orchard, Railroad, Haynes, and Warrior faults have the greatest displacement, which ranges from 150 to 800 feet, and are downthrown to the north or west. Additional information on these faults can be found in Anderson and Creasy (1958), Krieger (1965), and Lehner (1958).

Oak Creek, Sedona, Cathedral Rock, and Bear Wallow Canyon faults are the major faults in the Sedona area (pl. 1); all displace Paleozoic rocks. Oak Creek fault trends north-south and is downthrown 600 to 700 ft to the east (Twenter and Metzger, 1963, p. 64). The Sedona fault trends west-northwest and is downthrown 400 ft to the southwest (Twenter and Metzger, 1963, p. 64). Cathedral Rock fault trends northwest and is downthrown about 500 ft to the southwest (Twenter and Metzger, 1963, p. 65). Bear Wallow Canyon fault trends east-west and exhibits a maximum displacement of 170 ft downthrown to the south (Levings, 1980, p. 7). Additional faults that exhibit smaller displacements are found in the area, and volcanic flows probably cover even more faults. The rock units and overlying volcanic rocks, which are exposed in the canyons of Sycamore, Wet Beaver, and West Clear Creeks, contain many faults that do not offset the volcanic rocks. These faults trend northwest and exhibit variable displacements.

Fractures are common in the limestone and sandstone units that crop out in the area. Water travels along the fractures or faults, and enlarges fractures in the limestone by solution. Some solution channels are locally enlarged to caverns. The solution channels and caverns can store and transmit large quantities of ground water.