by 14 parts per million, seems to be due, in part at least, to the close proximity of the watering trough and corral to the well.

The water obtained from the Clark water shaft, from which Clarkstown (Rowood post office) has been supplied, is a calcium-sulphate water of high mineral content. It is unfit for boiler use and consumes excessive amounts of soap. The principal objection of consumers to this water has been a suspicion that it contains salts of copper, but a qualitative test failed to show the presence of copper.

From his well in Gibson Al Johns has been retailing water in Gibson and in Clarkstown in competition with water from the Clark water shaft. The well is dug through alluvium into rock along the main street of Gibson. The water has 562 parts per million of total dissolved solids, compared to 1,559 parts in the Clark water, and therefore is more pleasant to the taste. Like the Clark water, it gave no test for copper, but as the well is near dwellings it is subject to the possibility of pollution which always exists in such circumstances.

The well near the Black Prince mine, dug originally as a prospect hole, has a calcium-carbonate water with total dissolved solids of 1,091 parts per million. The water is hard and will need to be softened for use in laundry work. The organic matter is high, but this is probably due to trash and dead bees which, because the well is uncovered, fall into the water. The well will be a satisfactory source of water for prospecting, but the amount of water is insufficient for a large mine.

The water of Papago Well is a sodium-carbonate water of moderate mineral content and can be used for all purposes. The well is a drill hole of.considerable depth, and as the log is not known it may penetrate lava and not crystalline rock. The sample was taken from the well with a bailer and is water that had been standing in the well for some time. A small amount of hydrogen sulphide was found in the water. Sulphur in this form and in small quantities is not harmful and may be readily removed by aeration.

Analyses and classification of water from wells in crystalline compler

[Analyzed by A. A. Chambers and C. H. Kidwell. Parts per million except as otherwise designated]

WATER IN THE SEDIMENTARY ROCKS.

The sedimentary rocks in the Papago country are of three typeslimestone, shale, and quartzite of Paleozoic age; sandstone and shale of Mesozoic age; and conglomerate of Tertiary age (Pl. IX). The areas of outcrop of these formations are small, and only a few wells are known to have been sunk in any of them.

The limestone of Paleozoic age is well jointed, and at the surface the joints are open. It seems likely that rain water is readily absorbed and that wells of sufficient depth should obtain water in these rocks. The water will, however, be more heavily mineralized than that found in the crystalline rocks. Near Snyders Hill a 6-inch drilled well 500 feet deep in Paleozoic limestone encountered water at 200 feet. From this well 4,000 gallons was pumped daily during the construction of the county road in 1917.

So little is known of the Mesozoic sandstone and shale that no predictions as to their water content can be made. They occur, however, largely in the Tumacacori Mountains, an area which is

comparatively well watered and in which storage reservoirs can be profitably used. (See p. 141.)

The Tertiary conglomerate includes rocks that differ greatly in porosity, even in a single outcrop. The coarse-grained beds that are not too thoroughly cemented should, however, be good water bearers, and such beds occur in all the areas in which these rocks crop out. About 4 miles east of Walls Well is a dug well 5 feet square and 59 feet deep, in which water stands 7.2 feet from the surface. The surface rock is tuffaceous conglomerate interbedded with lava. This material is not greatly unlike other outcrops of conglomerate, except that it seems to be more porous. The yield of the well is not known, but it is certainly sufficient for prospecting, the purpose for which the well appears to have been dug.

WATER IN THE TERTIARY VOLCANIC ROCKS

The Tertiary volcanic rocks range in thickness from 50 to 2,000 feet and are composed of lava, tuff, and stream-laid conglomerate. The lava ranges from massive beds 50 to 300 feet thick with few joints or openings to beds laid down in plates 1 to 2 feet thick and having many joints. The rock of either the thick or the thin beds may be dense and compact or vesicular and scoriaceous. Some of the tuff beds are coarse grained and porous; others are so fine grained or so thoroughly cemented as to be impervious to water. The conglomerate likewise, though normally porous, may be cemented and impervious. A formation composed of rocks that differ so much in type and thickness obviously differs from place to place in its ability to absorb and hold water. In general, however, the surface layers are broken by numerous open joints, and in outcrops having a thickness of more than 200 feet there are usually beds of lava, tuff, or conglomerate having sufficient pores, vesicles, or joints to make excellent water bearers. The attitude of the bedding and the area and attitude of the outcrop are of prime importance to the prospective well driller.

Fortunately, the marked stratification of the rocks is generally not concealed by soil or vegetation, and the intelligent layman may therefore readily determine the essential factors. These factors may be summarized as follows: A large area of the rocks should be exposed to rainfall or a smaller area to flood waters; the exposed portion of the rocks should be porous or much fractured and should communicate by pores or fractures with the porous beds below; the lower part of the block of volcanic rocks should be below the general level of drainage, so as to make a reservoir that will hold ground water.

A relatively small number of wells draw water from the Tertiary volcanic rocks, though some of these are among the most successful in the Papago country.

The municipal supply of Ajo and the water necessary for the operation of the large mill and leaching plant of the New Cornelia Copper Co. at Ajo are drawn from No. 1 well, which ends in volcanic rock. In 1913 the New Cornelia Copper Co. drilled four wells in a search for an adequate supply for the town of Ajo and the company's projected plant. No. 1 well, near the north end of the Valley of the Ajo, gave the most promising results. The log showed about 200 feet of alluvium and below that alternating beds of various lavas to the bottom at 1,348 feet. Between 645 and 664 feet the log showed 19 feet of "gravel," which was water bearing. A test with an air lift yielded 200 gallons a minute, with no evidence of diminution in flow and so quick a recovery on the cessation of pumping that the drawdown could not be measured. Accordingly, work was begun on a two-compartment shaft 6 by 12 feet at a point 100 feet south of the drill hole. This was sunk to 651 feet. At 645 feet a pump chamber 21 by 41 feet and 14 feet high in the clear was cut south of the shaft, and a drift was run to the drill hole on the north. Another chamber was excavated to one side of the pump chamber as a sump. The apparatus installed consists of two vertical centrifugal pumps direct connected to vertical motors, which pump from the shaft to the sump. From the sump the water flows by gravity to the suction pipe of a double-acting cylinder pump direct connected to a motor. This pump lifts the water to the surface and thence through a pipe line to a 500,000-gallon tank on Reservoir Hill, above the mill at Ajo, 7 miles away. The pressure on the pump cylinders is about 590 pounds to the square inch, and the total lift including friction is 1,475 feet. The yield of the plant is 800 gallons a minute. The combined log of the shaft (to 651 feet) and well (from 651 to 1,438 feet) is as follows:

Log of Well No. 1, New Cornelia Copper Co.

Examination of the rocks in sinking the shaft revealed some of the errors in the well log. The alluvium is only 173 feet deep instead of 200 feet, and there are many variations in the character of the lava beds. The "gravel" shown in the original log was found to be a soft red lava. Detailed examination of this lava shows that it is a flow breccia and consists of irregular fragments of vesicular lava embedded in a matrix of finely porous lava. It is evidently a lava flow which when poured out on the surface contained gases that caused it to expand in a molten froth. This froth, congealing on the surface of the flow, was continuously engulfed in the unsolidified material below, until the whole flow consisted of rubble of partly solidified vesicular masses contained in a matrix of similar material. The rock is very porous, and many of the cavities are large. It is an ideal water bearer.

Two miles west of the Gunsight ranch, at the place known as Jaques ranch, is an old well. It was dug to supply water for the Gunsight mine during its period of activity from 1874 to 1882. It was 280 feet deep and cribbed with timber. The cribbing was burned, and the well was reopened by David Disque in 1914 to use the water for irrigation, but a flood from the arroyo near by caused the well to cave a second time. It was partly reopened in 1917 by Jaques & Para. In October, 1917, the well was 5 feet square, cribbed with lumber, and 166 feet deep, and the depth to water was 160.8 feet. The well is said to yield sufficient water to supply a windmill. The pile of waste thrown out of this well is mostly lava similar in type to that in the hills to the west, so that it seems certain that the water is derived mostly from Tertiary volcanic rocks that do not crop out. Cochibo (Pl. XXV) is a watering place belonging to José Manuel, a Papago, who dug two wells in 1913, 30 feet apart, at the bottom of a narrow canyon cut in Tertiary volcanic rocks on the east side of the Ajo Mountains. The north well is 14.9 feet deep and had water at 13.0 feet from the top of the curb, or 3 feet above the bed of the stream. These measurements were made on November 14, 1917, and at that time the adjacent rocks were damp, so that it seems likely that the wells were dug at a place where there has always been a wet-weather seep. The wells are dug in friable and intricately jointed flow breccia, which probably derives its water supply from the rain absorbed in the heavy talus of the mountain side to the south and from the infiltration of flood waters of the stream.

Only two analyses of water from wells in the Tertiary volcanic rocks were made in this investigation. The well of the United States Indian Service at Indian Oasis penetrates alluvium and then goes into volcanic rocks. The water is of the calcium-carbonate type and

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