Geological Survey Water-Supply Paper 1475-C Geology in Relation to Availability of Water Along the South Rim Grand Canyon National Park, Arizona

The ground-water resources of the Grand Canyon area are related to the lithology of the sedimentary formations and to the geologic structure. One of the important lithologic characteristics is the grain size. The rocks range from very fine grained clay through silt and sand to coarse gravel. Although clay and silt may contain large amounts of water, very little can move through them or drain from them, and consequently they offer little hope for the development of water. Another consideration is the degree of sorting—whether the sediment is made up essentially of one grain size or is a combination of grain sizes. If a sand is well sorted, it will transmit water readily and will have good storage capacity. Also, the amount of cement in the sedimentary rocks may be important. Well-cemented rocks hinder or completely block the movement of water. In limestone, the most important characteristic is the occurrence of solution channels. Most limestone is dense, and water will not move through the rock unless it contains solution channels.

Geologic structure also is important. The regional dip, monoclinal flexures, and faults control the movement and occurrence of ground water. In the Grand Canyon area the regional dip is small (1° to 2°) and water tends to move downdip on top of relatively impermeable layers. Where the regional dip is interrupted by monoclinal flexures, water may follow these flexures. Faulting may bring fine-grained rocks against permeable rocks and provide a dam against which water accumulates in the permeable rocks.

OCCURRENCE

Ground water in the Colorado Plateau occurs as a series of perched water bodies in permeable strata, as shown diagrammatically in plate 14. A rock unit that does not readily transmit ground water and prevents or retards the downward percolation of ground water is termed an aquiclude, or confining bed. The occurrence of an aquiclude beneath a permeable bed under favorable structural conditions provides conditions for the entrapment and storage of ground water. The principal formations constituting aquicludes in the Grand Canyon area are the Vishnu schist, the Bright Angel shale, and the Hermit shale (pl. 14).

The Vishnu schist and other Precambrian rocks generally form an aquiclude. Seeps were observed in many places along the contact between the Precambrian rocks and the Tapeats sandstone. They occur only where the Precambrian rocks are dense and are not much fractured and disintegrated. Locally, disintegration has created some porosity in the Vishnu schist, and some water seeps down into the schist.

Another important aquiclude in the Grand Canyon area is the Bright Angel shale. From Hermit Creek to Cottonwood Creek, numerous springs issue from the overlying Muav limestone along the top of the Bright Angel shale. The basal unit of the Muav limestone is a cliff-forming limestone about 30 feet thick (the Kanab Canyon member of McKee, 1945, p. 102), which contains numerous solution channels. Many of the springs, including the ones at Indian Garden, which yield about 300 gpm, issue from this unit. Where the Muav limestone has a large saturated thickness, springs issue higher in the formation. In Hermit Creek canyon it was observed that the uppermost spring of Hermit Creek issues from dolomite in the Muav immediately below the Redwall limestone. This spring yields about 1 gpm. Downstream, numerous springs were observed and the flow of the stream was larger. The flow where the stream crosses the Tapeats sandstone was measured at 210 gpm on May 8, 1958 by the Geological Survey.

The absence of springs in the Muav limestone in the Desert View area is attributed to structural conditions. The dip of the strata throughout the Upper Basin is southward at about 100 feet per mile except in the vicinity of the monoclinal flexures (pl. 13, cross section A—A'). Therefore, water probably moves southward toward the Grandview flexure, and as the upthrown Bright Angel shale is a hindrance to water moving in the Muav limestone, the water probably moves eastward along the flexure. The absence of springs along the rim indicates that not enough water is stored in the Muav limestone in the Upper Basin to overflow along the rim.

The only potential aquifer in the Desert View area is the Muav limestone. As no wells have tapped the Muav, its productivity is not known. However, there are three possibilities related to the occurrence of ground water in the Muav limestone in the Upper Basin:

(1) the Grandview section of the east Kaibab monocline on the south and the Waterloo Hill section on the east may impede the movement of water, causing it to accumulate in the Muav limestone and to "back up" toward, though not reaching, the canyon rim. (2) There are neither major barriers or local structural conditions to allow accumulation of water. (3) There is no major barrier, but local structures are favorable for ground-water storage.

If there are effective barriers to ground-water movement along the Grandview and Waterloo Hill flexures, ground water will occur in the Muav limestone along the base of the flexures and for some distance updip. If water is present, the amount that might be obtained would depend upon the number and size of the solution channels penetrated in the Muav.

If a barrier does not exist along the Waterloo Hill flexure and local structures that might trap water are missing along the Grandview flexure, there would seem to be little or no chance of developing locally the amount of water needed for Desert View.

The last possibility is that local structures along the Grandview flexure are favorable for ground-water storage, even if there is no barrier along the Waterloo Hill flexure. Such local structures would have to be nearly perpendicular to the Grandview flexure and would be in the form of either faults or monoclines. In either case the rocks would have to be lifted to the east. This would allow for storage of water in the Muav limestone against the Bright Angel shale, but the amount of storage probably would be small. It is doubtful if such local storage could produce the amount of water needed for Desert View.

Ground water occurs in the Redwall limestone only where the underlying Muav limestone is completely saturated. These conditions exist at only two localities along the south rim of the Grand Canyon—one at Blue Spring (fig. 23 and pl. 13) about 9 miles northeast of Desert View, and the other at Havasu Springs (fig. 23) about 30 miles northwest of Grand Canyon village. In both places, structure is a governing factor for the saturation of the rocks. The rocks in the vicinity of Blue Spring have been bent downward below the level of Desert View by the east Kaibab monocline. Thus, the Muav limestone is below stream level and ground water occurs stratigraphically higher in the Paleozoic section. Havasu Springs are structurally lower than Grand Canyon village because of the regional dip to the southwest. The rim is about 1,000 feet lower at Havasu Canyon than at Grand Canyon village.

Small deposits of travertine were observed along Hermit Creek, and it appears that the stream is still depositing the material. The uppermost spring in Hermit Creek is not very far below the Redwall limestone. Apparently the water from the Redwall is actively building up travertine deposits downstream from the outlets of Blue and Havasu Springs. The presence of travertine in Hermit Creek may indicate that some of the water has moved through the Redwall limestone. None of the springs that issue from the basal part of the Muav limestone have deposited travertine.

The Hermit shale in Hermit Basin is fine grained and forms an aquiclude. Two springs (pl. 13, Nos. 1 and 2) issue from the basal part of the Coconino sandstone, at the top of the shale. A stock well in sec. 21, T. 30 N., R. 1 W., southwest of Grand Canyon village, obtains water from the Coconino sandstone where the water is upheld by the Hermit shale. At this location, structural conditions are favorable for the entrapment and storage of water on the shale. The Hermit shale grades into more permeable siltstone and sandstone to the east, and in the Desert View area it cannot be readily distinguished from the Supai formation. Therefore, it does not act as a barrier to downward movement of water or allow storage in the Coconino sandstone. This fact is demonstrated by a dry hole drilled at the base of the Grandview flexure in sec. 5, T. 29 N., R. 6 E., into the red beds of the Supai beneath the Coconino sandstone that disclosed no water in the Coconino.

Small seeps occur in the Kaibab limestone where the downward movement of ground water is retarded by relatively impermeable beds. Rowes Well is an example. According to Mr. Art Metzger (oral communication) Rowes Well is shallow and was dug at a seep. Other small seeps were observed coming from the Kaibab limestone, but the amount of water available is very small. In dry years, little or no water would be available.

RECHARGE

The Kaibab limestone has, by far, the largest outcrop area of any formation in the Grand Canyon area. Outcrops of the other formations are much smaller and are restricted to the canyons of the Colorado and Little Colorado Rivers. Thus, the major part of the water that recharges the ground-water reservoir must percolate downward through the Kaibab limestone.

The greater part of the drainage area above Havasu Springs is on the Kaibab limestone. The discharge of these springs gives some indication of the amount of water that recharges the ground-water reservoir. Havasu Springs have a discharge of about 66 cfs (U.S. Geological Survey, 1954). If it is assumed that the underground drainage area contributing to the springs is the same as the surface drainage area of Havasu Creek, which may not be the case, the springs represent the natural discharge point for a drainage area of 2,900 square miles. This gives a discharge of 0.02 cfs per square mile of drainage area, or about 20 acre-feet per year per square mile, equivalent to about 0.3 inch of water per year over the entire drainage area.

According to U.S. Weather Bureau records, the amount of precipitation falling on the Havasu Creek drainage area ranges from about 10 to 20 inches per year, or about 500 to 1,000 acre-feet per year per square mile of drainage. Thus the amount of water infiltrating into the Kaibab limestone and later discharging from the ground water reservoir represents only a small fraction of the precipitation.

MOVEMENT

One of the most dominant controls on the movement of ground water in the Grand Canyon area is the geologic structure. In the Desert View area monoclinal flexures probably govern the direction of movement whereas to the west the Bright Angel fault exerts an influence on the movement.

Although there are no wells in the Desert View area, it is believed that the general ground-water movement can be ascertained from the geologic structure. The dip of the strata in the Upper Basin is southward at about 100 feet per mile, and the movement of ground water also is probably southward. The Grandview flexure probably forms an effective barrier to this general ground-water movement, as the Bright Angel shale and other formations of low permeability are upthrown across the path of movement. In all probability ground water turns eastward and parallels the flexure, crosses the northern sections of the east Kaibab monocline, and ultimately discharges through Blue Spring. Because of the large "throw" on the monocline that lowers the Muav limestone, the ground water seems to occur in the Redwall limestone as well as in the Muav, at least near Blue Spring, which discharges from the Redwall.

The occurrence of the springs at Indian Garden is due to a restriction of movement caused by the Bright Angel fault. The upthrow is to the west, bringing the relatively impermeable Bright Angel shale against the lowermost cliff-forming unit of the Muav limestone.

The many springs issuing from the Muav limestone in the stretch from Hermit Creek to Cottonwood Creek indicates that the direction of movement of ground water along the rim is northward. But there is no evidence as to how far south of the rim this direction is maintained. Surely there is a drainage divide south of the rim because the regional dip is southwestward. Sufficient data are not available from wells south of the canyon to give any indications as to the location of the divide.

DISCHARGE

Ground water discharges through springs in the Grand Canyon (table 1) and from a stock well south of the rim. Only small seeps. are found in the Kaibab limestone on the rim. The stock well in sec. 21, T. 30 N., R. 1 W. is the only well shown on figure 23 that was producing water during this investigation.

The springs that issue from the Coconino sandstone are Dripping Springs (pl. 13, No. 1) and an unnamed spring (pl. 13, No. 2) along the Hermit trail. Both springs are very small and yield less than 1 gpm. "Dripping Springs" is a good descriptive name, because the springs bearing that name occur in a recess under the Coconino sandstone and the water drips from the contact of the Hermit and Coconino.

Only one spring was observed that issues from the Supai formation. It is Santa Maria Spring and may flow as much as 1 gpm. The water seeps from sandstone about 20 feet thick.

Most of the springs issue from the Tonto group, at several stratigraphic positions. The stratigraphically highest springs within the Tonto group issue from the dolomites of the Muav limestone immediately below the Redwall limestone, where the spring flow forms Hermit Creek (pl. 13, No. 4). The Muav limestone is almost saturated at spring 4, and many other springs enter the creek from the Muav in the stretch downstream toward the Colorado River. The total flow was 210 gpm on May 8, 1958. Indian Garden Springs (pl. 13, No. 8) issue from the basal cliff-forming limestone of the Muav limestone. According to Park Service records, the flow is about 300 gpm. Some small springs occur in the Bright Angel shale (pl. 13, Nos. 15 and 16). Three springs (pl. 13, Nos. 5, 6, and 7) were observed to be issuing along bedding planes in the Tapeats sandstone, although Monument Spring (pl. 13, No 5) is supplied in part from other sources higher in the Tonto group.

One spring (pl. 13, No.9) issues from the Vishnu schist. The occurrence is related to a disintegration zone in the schist, and the water has percolated downward from the Tapeats sandstone.

Only two springs in the south-rim area between Hermit Creek and Cottonwood Creek yield significant quantities of water. Indian Garden Springs are the largest (about 300 gpm). Hermit Springs yield about 210 gpm. All other springs yield less than 10 gpm and most yield less than 1 gpm. The total flow from the springs is about 600 gpm.

Two large springs along the south rim are Blue Spring on the Little Colorado River and Havasu Springs in Havasu Creek (fig. 23). Blue Spring, which forms the perennial flow of the Little Colorado River, flow about 220 cfs and Havasu Springs, about 66 cfs. (U.S. Geological Survey, 1954). They issue from the Redwall limestone.

Description of wells in Coconino Plateau area, Arizona

Only one of the wells listed in the table and shown on figure 23 produced water in the spring of 1958. The well in sec. 21, T. 30 N., R. 1 W., was drilled in 1942 to a depth of 1,000 feet, and the water level was reported to be 900 feet below the land surface. Although the yield is not large, the water is reported to be satisfactory for stock use. The water tapped by this well is perched on the Hermit shale, and the ground-water reservoir is probably not very extensive. Farther south in sec. 3, T. 27 N., R. 1 W., the depth to water in an abandoned well in the Supai formation is 1,400 feet. Data are insufficient to determine whether the depth to water represents the regional water table or another perched water table.

PRESENT WATER SUPPLY AT INDIAN GARDEN

Two of the largest springs at Indian Garden are developed and piped to a storage reservoir. One of the springs issues from the slope east of Indian Garden and the other issues from the creek bed at the uppermost end of Indian Garden. The flow of the other small springs is not collected at Indian Garden; however, downstream, some of the water is collected and pumped to the storage reservoir at Indian Garden. The combined flow is then pumped to the south rim, a lift of 3,200 feet. At present, the Park Service operates a weir with recording gage downstream from the lower pumphouse, in order to determine the amount of water not being used.

RELATION OF SPRING DISCHARGE TO SIZE OF DRAINAGE BASIN

In the Colorado Plateaus there probably is a general relation between the discharge of springs and the size of the surface drainage basin above the springs. It has been observed that large springs generally discharge from large drainage basins, and vice versa. It would be desirable if this qualitative observation could be translated into a quantitative answer.

A related problem is the position of the ground-water divide between areas of ground-water discharge. In many places on the Colorado Plateau there are not sufficient data to locate a divide with any degree of accuracy. It is not known whether the movement of ground water in geologic time has been stabilized so that the ground-water and surface-water divides coincide at least approximately or whether the two divides are many miles apart.

Three springs along the south rim of the Grand Canyon—Blue, Havasu, and Hermit—may add evidence to the relation of spring discharge to size of drainage basin and, by inference, to the position of the ground-water divide between areas of discharge. Pertinent facts concerning the three springs are given in the following table:

The springs have a large range in discharge, the ratio of largest to smallest being 440 to 1; and a large range in surface drainage area, the ratio being 2,300 to 1. However, the discharge per unit drainage area shows a small range, the ratio being only 4 to 1.

Geologically, the drainage areas above Havasu and Hermit Springs are similar—both are on Paleozoic rocks (Kaibab limestone). Blue Spring are in the drainage area of the Little Colorado River, and the surface geology is much different from that of the other two areas. Also, there are other points of ground-water discharge, and not all the available water issues from Blue Spring.

If the springs represented all the ground-water discharge and if the drainage divides for both ground water and surface water coincided, the figures of 0.01, 0.02, and 0.04 cfs per square mile would represent the approximate recharge to the ground-water reservoir. The discrepancy in recharge between Blue and Havasu Springs could be explained as due to the difference in geologic environments, as well as the presence of other ground-water outlets in the Little Colorado drainage area, but because of their geologic similarity the discrepancy in recharge between Havasu and Hermit Springs could not be thus explained. It is tentatively concluded that the ground-water and surface-water divides do not coincide, or that the discharges and drainage areas of Havasu and Hermit Springs are too different to permit a direct comparison on a unit-area basis.

QUALITY OF WATER

Fourteen samples of water from springs along the south rim were analyzed for their mineral Content. These analyses, and analyses for Blue and Havasu Springs also, are given in table 1. The waters, with the exception of that of Blue Spring, are all of good chemical quality, although they are hard, and are satisfactory for domestic use according to the standards for drinking water of the U.S. Public Health Service. The dissolved solids in the 14 samples from the report area ranged from 179 to 667 ppm; only 2 samples contained more than 400 ppm.

TABLE 1.—Chemical analyses of water from springs, Grand Canyon area, Arizona
[Chemical constituents in parts per million except as indicated. Discharge: <, less than; E, estimated; M, measured; N, see remarks]
[Analyses by U.S. Geological Survey, Albuquerque, N. Mex.]

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

An inspection of the analyses indicates that along the south rim, as the water percolates downward (pl. 14), there is an increase in mineral content of the water. The water from the Coconino sandstone has 179 and 194 ppm of dissolved solids, from the upper part of the Muav limestone 239 ppm, from the rest of the Muav 248 to 387 ppm, and from the Tapeats sandstone 540 and 667 ppm. It has been mentioned previously that there are "salt seeps" issuing from the Tapeats sandstone. These are very small and no samples were collected. It may be postulated that the quality of water from these seeps is not as poor as would be suggested by the presence of the salt stalactites and stalagmites, for some of the concentration of this mineral content leading to salt deposition doubtless is due to evaporation of the small quantities of water seeping from the rocks.

PLATE 14.—COLUMNAR GEOLOGIC SECTION NEAR GRAND CANYON VILLAGE, ARIZONA, SHOWING THE STRATIGRAPHIC POSITION OF SELECTED SPRINGS. (click on image for an enlargement in a new window)