Geological Survey Water-Supply Paper 1475-J Ground Water in the Wupatki and Sunset Crater National Monuments, Coconino County, Arizona

The rocks of the Wupatki-Sunset Crater area are composed of Permian and Triassic formations, overlain in part by a series of younger volcanic rocks and alluvial deposits principally of Quaternary age. The oldest formation exposed is the Coconino sandstone; however, some of the deeper wells penetrate the underlying Supai formation at depths of more than 1,000 feet below the land surface. No formations older than the Supai are discussed in this report.

The Kaibab limestone of Permian age and the Moenkopi formation of Triassic age crop out in most of the Wupatki National Monument, and there are also small outcrops of the Coconino sandstone, the Toroweap formation, and Quaternary volcanic rocks and alluvial materials. The strata dip gently to the northeast, but this regional dip is interrupted by a transverse fold known as the Black Point segment of the East Kaibab monocline. In the northern part of the area the monoclinal flexure has a southerly strike, but within a few miles it changes to a southwesterly strike. Here the monocline steepens and grades into a fault that can be traced to the edge of Doney Crater. This fault has a displacement of more than 150 feet. Small northeast- and northwest-trending faults and grabens displace the Kaibab limestone on Antelope Prairie (Babenroth and Strahler, 1945, pl. 2), but they are not shown on the geologic map (pl. 20).

In the vicinity of the Sunset Crater National Monument, the volcanic rocks and associated alluvium completely cover the underlying sedimentary rocks and mask the structural pattern. However, structural relations can be observed along the north and east fringes of the volcanic field, where the underlying rocks are exposed. The diagrammatic cross section B—B' on plate 20 is based on the projection of these relations. The alinement of the volcanoes suggests the presence of zones of structural weakness in the rocks underlying the volcanic field, but in the absence of specific field evidence the nature and location of such zones are not indicated on the cross section. The generalized structure contours shown on figure 45 indicate a broad, shallow trough, plunging to the northeast from Flagstaff to Wupatki Ruin on the east side of the Black Point segment.

FIGURE 45.—Map of north-central Arizona, Wupatki-Sunset Crater area, showing major structural features, structure contours, and direction of ground-water movement. (click on image for an enlargement in a new window)

SEDIMENTARY ROCKS

PENNSYLVANIAN AND PERMIAN ROCKS

SUPAI FORMATION

The Supai formation consists mostly of brownish-red fine-grained sandstone and siltstone and some thin beds of limestone. It is about 750 feet thick on the east slope of Elden Mountain (Brady, 1934, p. 10), about 10 miles south of the Sunset Crater National Monument. A study of well cuttings revealed that the upper 480 feet of the formation is a very fine grained to fine-grained, fairly well sorted to well-sorted friable sandstone. In Oak Creek Canyon, about 25 miles south of Flagstaff, the upper part of the Supai formation contains large-scale crossbeds and is a transitional zone between the more typical flat-bedded units and the overlying highly crossbedded Coconino sandstone. The Supai formation yields water to well (A-22-10)3ad in the southeastern part of the area (table 1). The formation also yields water to a well at the Navajo Ordnance Depot, 12 miles west of Flagstaff.

TABLE 1.—Records of selected wells and springs in Wupatki-Sunset Crater area, Coconino County, Ariz.
[C, cylinder; G, gasoline; D, domestic; S, stock; N, not used.]

(click on image for an enlargement in a new window)

PERMIAN ROCKS

COCONINO SANDSTONE

The Coconino sandstone is a very pale-orange to grayish-orange, very fine to fine-grained friable sandstone composed of well-rounded quartz grains; it is crossbedded on a large scale. The degree of cementation varies, but most of the sandstone is firmly bonded. The thickness of the formation ranges from about 600 feet in the Elden Mountain area (Brady, 1934, p. 10) to a possible 1,035 feet near the north boundary of the Wupatki National Monument, as reported in the driller's log of well (A-26-9)33dd (table 2). Due to the difficulty in identifying the formations from well cuttings, this excessive thickness may include part of the upper sandy zone of the Supai formation. In this report the Coconino sandstone and the overlying Toroweap formation are undifferentiated, and have been mapped as a single unit (pl. 20). The Coconino sandstone is the main aquifer in the area, and at least five deep wells obtain water from it.

TABLE 2.—Logs of selected wells in the Wupatki-Sunset Crater area, Coconino County, Ariz.
[Drillers' logs, except (A-22-10)3ad, geologist's log, and (A-23-8)20aa, owner's log]

KAIBAB LIMESTONE

The Kaibab limestone is a thick-bedded, jointed, very pale orange cherty and sandy limestone that crops out extensively in the Wupatki area. It overlies the Coconino sandstone, or the Toroweap formation where present, and ranges in thickness from about 300 feet near Elden Mountain (Brady, 1934, p. 10) to about 365 feet north of Wupatki National Monument, as reported in the driller's log of well (A-26-9)33dd (table 2). In this area the Kaibab limestone is not an aquifer, as it is above the water table. Where it is exposed the Kaibab limestone, because of its jointed nature, absorbs water and is an important recharge medium.

TRIASSIC ROCKS

MOENKOPI FORMATION

The Moenkopi formation was deposited unconformably on Kaibab limestone. It is generally reddish brown and consists of flat, very thin to thick layers of siltstone, mudstone, and sandstone; lenticular beds and thin stringers of gypsum are common in the middle part of the formation. The particles within the individual beds are for the most part composed of fine, poorly sorted quartz sand and are cemented with varied amounts of calcareous, or more rarely ferruginous and gypsiferous, material. Where it crops out in the eastern part of the area, the Moenkopi formation ranges in thickness from a few feet to more than 300 feet; in the western part of the area the formation is less than 100 feet thick. This range in thickness is due chiefly to postdepositional prelavaerosion.

The Moenkopi formation does not transmit water readily in the Wupatki-Sunset Crater area because of its small average grain size, poor sorting, and alternation of nearly impermeable siltstone, mudstone, and sandstone beds. In addition, south of the Little Colorado River it is above the regional water table. In some areas, as at Heiser and Wupatki Springs, impermeable beds within the formation have prevented the downward percolation of water, and a perched water table exists. All the springs in the area yield less than 1 gpm; all issue from joints and bedding planes in the sandstone units.

CHINLE FORMATION

The Chinle formation overlies the Moenkopi formation and crops out along the northeast side of the Little Colorado River (pl. 20). Its lower part consists of brownish- to pinkish-gray poorly sorted sandstone and conglomerate, bonded with varied amounts of siliceous cement. The lower part formerly was a separate formation, the Shinarump conglomerate, but it is now considered the Shinarump member of the Chinle formation. The upper part of the Chinle formation is composed of variegated mudstone, siltstone, and sandstone assigned to the Petrified Forest member. The Chinle formation does not occur southwest of the Little Colorado River.

QUATERNARY DEPOSITS

GLACIAL OUTWASH

In the southwest corner of the area, glacial outwash from San Francisco Mountain locally overlies the volcanic rocks of the second general period of eruption and underlies and intertongues with the basalt flows of stage III (Robinson, 1913, p. 38; Childs, 1948, p. 362-364). (See B—B', pl. 20.) The best exposures of glacial outwash are west of Bonito Park in the Sunset Crater area. The outwash consists of unconsolidated sediments ranging in size from boulders to clay particles and in thickness from a few feet to more than 100 feet. Lenses and beds of coarse sand and gravel are present, but their extent and permeability are unknown. The coarse beds probably contain small amounts of perched water where they are underlain by impermeable material. A shallow well in glacial outwash gravel west of U.S. Highway 89 furnishes water for a highway maintenance camp.

CONGLOMERATE

One small area of volcanic conglomerate crops out northwest of Merriam Crater in the southeast corner of the area. This conglomerate is between basalt flows of stages I and III. It is well cemented by calcareous material and composed of poorly sorted rhyolitic to basaltic volcanic fragments which range in size from silt to cobbles. The character of the conglomerate and its altitude above the water table make it a doubtful source of ground water.

ALLUVIAL FANS AND STREAM-CHANNEL DEPOSITS

The valley floor of Deadman Wash in the western part of the area is underlain by alluvium, which in some places is at least 65 feet thick, as shown in the driller's log of well (A-24-8)29ab (table 2).

The other washes in the area contain small amounts of alluvium, and in many places small tributaries have built alluvial fans into the channels of the larger washes. There is also a considerable amount, possibly more than 75 feet, of alluvium along the Little Colorado River where it passes through the area. It is not known to contain usable amounts of ground water, although, between Black Falls and Cameron, the drilling of test holes for uranium prospecting has tapped water in the alluvium. All the alluvial deposits range in age from late Pleistocene to Recent.

ALLUVIAL FILL IN SMALL BASINS

Bonito Park in the Sunset Crater National Monument is a basin partly filled with alluvium whose total thickness is not known, although about 300 feet of fill is present south of Sunset Crater in Doney Park. Well (A-23-8)20aa, dug in sand and gravel of the alluvium, yielded some water at 30 feet. When the well was deepened to 60 feet the water drained away and was lost to the well. Therefore, it is known that there are perched-water zones in the alluvium, but it is believed they contain only minor quantities of ground water.

Several basins in the vicinity of Citadel Ruin, formed by the collapse of underground solution channels, have been filled with alluvium and cinders. The fill in these basins may be as thick as 100 feet, and small amounts of perched water may be obtained where the permeable deposits are underlain by impermeable beds.

EXTRUSIVE IGNEOUS ROCKS

The extrusive igneous rocks in the Wupatki-Sunset Crater area are divided according to the work of Robinson (1913, p. 38) and Childs (1948, p. 362-364), into three main groups: stages I and II basaltic flows and cinders of the first, or oldest, period of eruption; intermediate to acidic flows with associated pumice and tuff of the second period of eruption; and Stages III and IV basaltic flows and cinders of the third, or youngest, period of eruption. Stages I and II basalts range in age from late Pliocene to middle Pleistocene, and stages III and IV range in age from late Pleistocene to Recent. The silicic flows range from early to middle Pleistocene but some were deposited contemporaneously with the stage III basalts.

BASALT FLOWS OF STAGES I AND II

The basalts of stages I and II were extruded on erosion surfaces cut on the Kaibab limestone and Moenkopi formation. They are exposed principally along the edges of the volcanic field, where they extend beyond the mantle of the younger flows. Stages I and II basalt flows are similar in composition, and their combined thickness is reported by Robinson (1913, p. 38) to range from 25 feet to 200 feet. The basalts are highly fractured and faulted, with displacements of less than 75 feet; if and where they extend below the water table they are likely to be good aquifers.

ROCKS OF SECOND PERIOD OF ERUPTION

The silicic volcanic rocks—composed mainly of andesite, dacite, and rhyolite—of the second period of eruption are exposed on the flanks of O'Leary Peak and west of U.S. Highway 89 on the slope of San Francisco Mountain. The rocks are not as highly fractured as the underlying basalts and possibly would not yield substantial amounts of ground water to wells. They may form an impermeable barrier to the downward movement of ground water where covered by alluvial sediments,

BASALT FLOWS OF STAGES III AND IV

Basalt flows of stages III and IV are widely exposed in the southern part of the area and as far north as the Doney Crater. They are distinguished from flows of stages I and II by their rough, unweathered, fresh surfaces. Although these basalts are highly fractured, their position above the water table precludes their consideration as a source of ground water.

CINDER CONES AND CINDERS

Numerous cinder cones, some of which rise about 1,000 feet above the surrounding land surface, occur in the southern part of the mapped area. Deposits of cinders occur also at Doney Crater, near Wupatki Ruin. There are cinders corresponding in age to all four stages of the basalt flows, but the cinders are not differentiated on the basis of age in this report. In the Sunset Crater area the flows of stages III and IV are covered nearly everywhere with layers of basaltic cinders, which range in thickness from a few inches to several tens of feet. Thin weathered zones and some deposition of calcium carbonate occur locally at the top of some of the cinder beds. Many small exposures of basalt flows, which have not been mapped separately, occur within the area covered by cinders. The cinders are highly permeable and conducive to ground-water recharge, but their general altitude above the water table makes them a doubtful source of ground water in this area.