Geological Survey Bulletin 845 Guidebook of the Western United States: Part F. Southern Pacific Lines

FIGURE 51.—Map showing route of Apache Trail, Ariz. (click on image for an enlargement in a new window)

DETOUR BY THE APACHE TRAIL

A most picturesque chapter is added to the transcontinental trip by the detour over the Apache Trail. (See fig. 51.) The distance is 120 miles in all and requires about one day in time and certain extra expenses for bus fare and hotel stop. This additional time and expense are well justified, however, by the superb scenery and the thrilling character of the trip.

Westbound passengers diverge from the main line at Bowie, proceeding by a branch railroad (through sleeper) to Globe and thence by auto bus to Phoenix, where the main line is rejoined. This detour is equally easy in the reverse order for eastbound passengers, who leave the main line at Phoenix and rejoin it at Bowie. The best features of this trip may also be seen by a circuit in private conveyance from Tucson over excellent highways across the highly picturesque Santa Catalina, Mescal, and Pinal Mountains, up the canyon of the Gila River to Globe and thence over the Apache Trail to Phoenix (or the reverse order). The geologic features on this line of travel are especially interesting. A comprehensive 1-day trip can be made from Phoenix to the Roosevelt Dam or even to Globe, and return, and in this trip duplication can be avoided by making the return journey to Phoenix over a perfect highway crossing the mountains from Miami to Superior and thence to Phoenix. All these trips eliminate the less interesting part of the journey, between Bowie and Globe.

From Globe to Phoenix the route is a fine highway following the old Apache Indian trail across Pinal Mountain, past the Roosevelt Reservoir, down the Salt River Canyon, through a very rugged region south of that river, past Superstition Mountain and across the Salt River Valley irrigation district. The scenery is most impressive and the geology is of great interest.

From Bowie the branch railroad descends the broad alluvial plain of the San Simon Valley to the prosperous old Mormon settlements about Safford, Solomonsville, and Thatcher. On the west is the high granite range of the Pinaleño Mountains with their culminating peak, Mount Graham, rising about 6,000 feet above the valley. On the east are the Peloncillo Mountains, consisting of a great succession of lavas and volcanic tuffs of Tertiary age lying nearly horizontal or tilted to various low angles and presenting steplike cliffs and rounded summits.

Near Solomonsville the Gila River is reached. This large stream occupies the center of a broad alluvial valley from Solomonsville to a point 75 miles northwest, where it enters a deep canyon at the Coolidge Dam. In the upper part of the valley the river water is extensively utilized for irrigation so that about Safford⁴⁹ there are wide areas of verdant fields of alfalfa, corn, and other crops, and numerous orchards and shade trees. Water is also derived from wells and from Merijilda Canyon, south of Safford. Much honey is produced. The early developments in the region were made by Mormon colonists, who had a hard struggle with Indians, floods, and other difficulties. A large proportion of the present population of the region, which is about 10,000, consists of descendants of these original settlers.

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⁴⁹Named for A. P. K. Safford, governor of the Territory from 1869 to 1877.

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From Safford northwest the railroad follows the southwest side of the Gila River, passing through an extensive irrigation district about the towns of Thatcher, Central, Pima, and Fort Thomas. In this region are many remains of dwellings and pottery of aborigines who used the water of the Gila River for irrigation many centuries before the coming of the white man. To the north is the high ridge of the Gila Mountains, made up of great flows of lava and deposits of volcanic tuff, agglomerate, and ash extending north to the White Mountains, which were the center of eruption of a vast amount of volcanic matter in Tertiary time. To the west are many high mountains consisting mostly of granite of pre-Cambrian age. About 11 miles north of Pima are hot springs, probably rising along a fault at the foot of the Gila Mountains. At Fort Thomas was an old frontier fort. At Geronimo the route enters the San Carlos Indian Reservation, 55 miles wide and occupied by 2,715 Apache Indians, a district of valley and mountains with considerable good land along the wide alluvial flats adjoining the Gila River. The lower part of the valley in the center of the reservation, however, is flooded by the great San Carlos Reservoir created by the Coolidge Dam, which is built in a narrow canyon in the Mescal Mountains. The dam, completed in 1927 at a cost of $5,500,000, was constructed by the United States Commissioner of Indian Affairs to control water for the irrigation of the Gila River Indian Reservation and the adjoining region west of Florence and about Coolidge, Casa Grande, and Sacaton. According to the records in the office of the Commissioner the dam, which is of novel construction, consists of three domes supported by two buttresses, is 250 feet high and 920 feet long, and has a spillway capacity of 120,000 second-feet. The reservoir is about 25 miles long and in places 4 miles wide and has a capacity of about 1,200,000 acre-feet of water. This amount is sufficient to cover 100,000 acres to a depth of 12 feet, which is four times the volume required for one year's irrigation in the Casa Grande Gila Reservation region. Below the dam is a power plant using two 7,500-horsepower turbines. This dam is barely visible from the railroad, which now skirts the north and east margins of the reservoir, but it is crossed by the highway from Bowie to Globe. At its abutments are fine exposures of eastward-dipping limestones of Carboniferous age.

San Carlos, long known as Rice, is at the confluence of the San Carlos River and Aliso Creek, two streams which also supply water to the San Carlos Reservoir. On both sides of the valley here are lava-capped mesas, and a short distance east is the old volcanic vent known as the Triplets. From San Carlos the valley of Aliso Creek is ascended. To the south are the high granite ridges of Hayes Mountain, capped in part by an extensive succession of strata of the Apache group. (See fig. 52)

FIGURE 52.—Section across the center of Hayes Mountain, southwest of San Carlos, Ariz.

Some of the Apache and overlying limestones are exposed in cuts of the railroad 6 miles west of San Carlos. To the southwest are the Pinal Mountains (pee-nahl'), consisting of granite and schist and culminating in Pinal Peak (elevation 7,850 feet).

Passing out of the Indian reservation about 12 miles west of San Carlos, the railroad crosses the gravel-filled divide between the Gila and Salt River drainage basins and descends a short distance to Globe.

The old mining town of Globe owes its existence and sustenance mainly to the Old Dominion copper mine, the workings of which extend far under the hills on the north side of the valley, in the northern part of the town. This mine has been in operation since 1877, producing a large amount of copper, much of it from rich ore that has been smelted, as is indicated by the great terrace of black slag near the mine.⁵⁰ The ore is in rocks of the Apache group, especially the Mescal limestone, which are invaded by large dikes and sills of diabase intruded in molten condition in pre-Cambrian time. Lying unconformably above the Apache rocks are sandstone of Cambrian age, limestone of Devonian and Carboniferous age, and a capping of dacite, a light-gray massive volcanic rock of Tertiary age that is conspicuous on the slopes near the mine. The area is traversed by many faults. The mine is very wet; in 1928 it was necessary to pump 5,000,000 gallons a day. Part of this water is sold for use at Miami and elsewhere. There are smaller mines north of Globe which have yielded considerable copper. Globe was established in 1876 and named from a nearby mining claim. (See figs. 53, 54.)

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⁵⁰According to the U. S. Bureau of Mines the production of ore at this mine to 1929 was 415,890 tons, averaging 2.65 per cent of copper and yielding about 18,943,000 pounds of dividends of copper, together with considerable gold and silver. Most of the ore is now mined from 2,400 to 2,600 feet below the surface. According to the Mines Handbook for 1931 this mine paid $14,405,260 from 1905 to 1918 and $2,477,750 from 1919 to 1929.

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FIGURE 53.—Section of region near Globe, Ariz. By Ransome and Darton

FIGURE 54.—Outline geologic map of Globe-Miami mining region, Ariz. By F. L. Ransome

Globe is in a region of great archeologic interest, for many remains of prehistoric structures and implements have been found here, and on the Healy terrace, on the edge of the city, an old dwelling has been uncovered.

From Globe busses convey passengers over the Phoenix highway, generally known as the Apache Trail. The first conspicuous feature is a ridge of gravel (old valley fill), which is crossed just south of the Old Dominion mine. The road passes about 2 miles east of the great copper camp of Miami, where copper is extracted by acid leaching from altered schists and other rocks that carry the metal in small percentage. Great piles of tailings of pulverized rock are a conspicuous feature. According to the United States Bureau of Mines, in 1929 this camp produced 166,357,360 pounds of copper from 10,817,567 tons of ore in which the copper content ranged from 0.83 to 1.1 per cent. The ore here is predominantly chalcocite; that at the Old Dominion mine in Globe contains also chalcopyrite, borite, and pyrite. The road descends the valley of Pinal Creek for some distance past outcrops of dacite lava and rocks of the Apache group broken by many faults. (See fig. 55.) Beyond the small irrigation settlement of Wheatfield the north end of the Pinal Mountains is crossed. This ridge here consists mainly of coarse granite (probably pre-Cambrian), which to the north is capped by heavy lava flows of Tertiary age. From the summit, which is in a high saddle (elevation 3,980 feet), there is a fine view of the valleys of the Salt River and Tonto Creek (tone'toe), now flooded for many miles by the Roosevelt Reservoir.

FIGURE 55.—Section showing relations of Apache strata 7 miles northwest of Miami, Ariz. By F. L. Ransoms

The broad old valley of the Salt River is floored and in part margined with valley fill consisting mostly of gravel and sand, part of it bedded, and some fine sediments probably deposited in a lake. The lake deposits are well exposed in badlands north of Roosevelt. As the road approaches Roosevelt there is a good view of the extensive Tonto cliff dwellings of aborigines in a deep alcove high in the cliffs about 2 miles southwest of the road. (See pl. 28, A.) One of them is a three-storied building, and there are also smaller structures, all of which have been abandoned for many centuries. There are also ruins of cliff dwellings in the Sierra Ancha, on the north side of the Salt River Valley. This high range of ridges and plateaus consists of a thick succession of strata of the Apache group invaded by intrusive silts of diabase, as shown in Figure 56. Certain layers of the Mescal limestone have been altered to the chrysotile variety of asbestos, which has been mined extensively for commercial use. Some of the refuse heaps at the workings are plainly visible from the road, as great white streaks high on the mountain slope. The value of this mineral varies greatly with quality. According to the Bureau of Mines the prices in 1931 ranged from $10 to $400 a ton.

FIGURE 56.—Section through Sierra Ancha, 15 miles northeast of Roosevelt, Ariz.; d, Dripping Spring quartzite; b, Barnes conglomerate; p, Pioneer shale; s, Scanlan conglomerate

PLATE 28.—A (top), CLIFF DWELLINGS, TONTO NATIONAL MONUMENT, 2 MILES SOUTHEAST OF ROOSEVELT, ARIZ. B (bottom), ROOSEVELT DAM AND RESERVOIR, ARIZ. Apache Trail at right; Sierra Ancha in distance; ledges of Mescal limestone and overlying strata at left.

A short distance beyond the small village of Roosevelt the Roosevelt Dam (pl. 28, B) is reached. It is built across the entrance of the long, deep canyon cut through the mountains by the Salt River just below the confluence of Tonto Creek. The Salt River rises in the mountains of eastern Arizona, where there is a moderately large rainfall and much snow. Its volume varies considerably from year to year; in 1914 the flow into the reservoir was 629,500 acre-feet, and in 1915 it was 1,440,100 acre-feet (U. S. Bur. Reclamation). Tonto Creek drains an extensive district north of the reservoir but has a much smaller flow than the Salt River. The reservoir when full is 15 miles long and from 2 to 4 miles wide and provides water for the irrigation of the Mesa-Phoenix region, 70 to 80 miles west of the dam.

This project was one of the early ones of the United States Bureau of Reclamation. At the time the work was begun in 1903 the region was inaccessible, so that roads had to be built, a cement mill erected and a plant constructed for development of power from a canal taken out of the Salt River 19 miles above the dam site. Much of the work was done by Apache Indians. (See pl. 29, A.) The dam was completed in 1911 and dedicated by ex-President Theodore Roosevelt on March 18 of that year. According to the United States Bureau of Reclamation it is 1,125 feet long and 280 feet high (to the roadway), with great spillways, in all requiring about 340,000 cubic yards of masonry. The power plant develops as much as 10,000 kilowatts, which is transmitted to the Phoenix region on three wires carrying 45,000 volts and with a capacity of about 21,000 horsepower. The total cost of the dam and power plant was $3,890,187. The reservoir has a capacity of 1,637,000 acre-feet. Other dams farther down the river, at Horse Mesa, Mormon Flat, and Stewart Mountain, add about 20 per cent to this capacity and treble the electric power. These features completely control the Salt River, which formerly wasted flood waters that caused devastation in the lower country. From these dams water is let out as needed, and the supply is sufficient for the irrigation of 242,000 acres. The canals and laterals aggregate 1,020 miles. About 800 rural homes in the valley are supplied with electricity. The total cost of the Salt River Valley project has been about $10,000,000.

PLATE 29.—A (top), ENCAMPMENT OF APACHE INDIANS ON BANK OF ROOSEVELT RESERVOIR. These Indians did much the construction work on the dam and the Apache Trail. Sierra Ancha in distances. B (bottom), VIEW ACROSS CANYON LAKE INTO CANYON OF SALT RIVER, 35 MILES EAST OF PHOENIX, ARIZ. Apache Trail in foreground; Four Peak (Mazatzal Mountains) in distance. The cliffs are volcanic tuff.

At the dam are great rock walls exhibiting one of the finest known sections of the Apache group, which lies on pre-Cambrian granite and is overlain unconformably by sandstones and limestones of Cambrian, Devonian, and Carboniferous age. (See fig. 57.) The strata dip eastward, and the hard quartzites form the crest and east slope of a high mountain range, the northern part of which is known as the Mazatzal Mountains (mah-zat-zahl', Indian word for red rocks). The river has excavated a canyon nearly half a mile deep across this range, which has been uplifted since the stream has flowed in its present course.⁵¹ The range is a long up-tilted block of the earth's crust, west of which the pre-Cambrian rocks occupy a wide area, in part overlain by Tertiary volcanic rocks.

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⁵¹The section begins a short distance below the dam and extends to the quarries southeast of the dam. The contact of the pre-Cambrian granite and the Scanlan conglomerate, the basal formation of the Apache group, is clearly exposed on the road as well as in the north wall of the canyon, a short distance below the dam. The Spring formation, next above, is a reddish quartzite, in part slabby, but so hard and compact that it makes the mountain crests to the north and south on both sides of the dam. It is invaded by thick sills of Algonkian diabase of a type distinctive of the Apache group in central Arizona and of the Unkar group in the Grand Canyon. The dam is built mainly in the Mescal limestone, which here attains its maximum thickness of 350 feet. Much of this limestone is pure but some beds contain considerable interbedded chert in thin layers, possibly of algal origin. On the Mescal lies a sheet of lava (basalt), vesicular in large part, especially at the top and bottom, and apparently conformable. This was a surface lava flow in late Apache time. The overlying sandstone (Cambrian), about 200 feet thick, contains at the base pebbles of the lava and other rocks, and though conformable in attitude it is separated from the Apache group by a great interval of geologic time. It is overlain by limestones and sandstones (Martin limestone) with Devonian fossils, and this in turn by limestone and sandstone of Carboniferous age, which are well exposed in ledges and quarries above the dam.

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FIGURE 57.—Section at Roosevelt Dam, Ariz.

Below the Roosevelt Dam the road descends the Salt River Canyon along its south side, crossing a wide area of the old granite that underlies the Apache group near the dam. In places, especially at points a few miles west of the dam, this granite is invaded by thick dikes of diabase that doubtless were feeders of sills in the Apache group, which probably formerly overlay the granite in this area also. The sahuaro, or giant cactus, is conspicuous here and in the country to the west. (See p. 179.) The narrow depths of the canyon in this vicinity are occupied by Apache Lake, a long picturesque reservoir held by the Horse Mesa Dam, built in 1926 in a tight canyon cut by the Salt River through the rhyolite at the west end of Horse Mesa, 17 miles below the Roosevelt Dam. According to the Bureau of Reclamation the Horse Mesa Dam is 305 feet high (bedrock to top of coping) and 540 feet long. The head of 264 feet gives about 43,000 horsepower. The lake has a storage capacity of 245,000 acre-feet. The highway skirts the lake but does not reach the dam.

Six miles below the Roosevelt Dam, where the road climbs onto a high spur, and at various other points in the next few miles there are fine views of Apache Lake and its high encompassing cliffs of volcanic rocks. These rocks belong to the succession that lies in a syncline constituting the southwest flank of the Mazatzal Mountains, Horse Mesa, and the highlands south of Apache Lake. (See fig. 58.)

FIGURE 58.—Section showing relations of Tertiary volcanic succession 15 miles southwest of Roosevelt Dam, Ariz. Tr, Rhyolite tuff; Ta, andesite; Agr, granite

In this region there are many fine views of Four Peaks (elevation 7,645 feet), in the Mazatzal Mountains to the north, and of the ridges capped by Apache or volcanic rocks to the south. The Four Peaks are also visible from many points westward to Phoenix. The Mazatzal Mountains contain deposits of quicksilver ore of low quality but of considerable extent which may prove to be of economic importance. They are in schists of pre-Cambrian age.⁵²

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⁵²Ransome, F. L., U. S. Geol. Survey Bull. 620, pp. 111-128, 1916.

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About 14 miles below the Roosevelt Dam the highway crosses a low divide, leaving the Salt River Valley, and passes into the valley of a branch of Fish Creek. Here in a short distance the granite is hidden by the volcanic succession just mentioned, of which the lower members (andesite or latite) are dark gray to bright red. These are overlain by a 2,000-foot succession of light-colored tuffs, agglomerates, and lava flows (largely rhyolite), most of which are so hard and massive that they present huge cliffs. These are especially prominent on Fish Creek, as shown in Plate 30, and in the canyon of the Salt River, both of which have cut deeply into them. There are fine exposures of these rocks on the ascent on the west side of Fish Creek, where the road climbs nearly 800 feet to gain the summit of the principal massive member, and also on the wide upland westward, which the road traverses on the divide between Fish Creek and Tortilla Creek. In a cavern called Hip Pocket, on the slopes near Fish Creek, American troops under General Crook cornered a band of outlaw Apaches and destroyed them all, in part by rolling stones onto them from the cliffs under which they were hiding.

PLATE 30.—VIEW UP CANYON OF FISH CREEK AT CROSSING OF APACHE TRAIL, 40 MILES EAST OF PHOENIX, ARIZ. Cliffs of volcanic tuff.

As shown in Figure 58, the principal structural feature in this vicinity is a shallow syncline, which is plainly visible along the road for a long distance west. Tortilla Creek exposes the dark basal member of the succession. Mormon Flat, the lower part of the valley of this creek, at its junction with the Salt River, is flooded by the reservoir known as Canyon Lake (pl. 29, B), which is held by a dam built in 1923-1925 in a bend of the Salt River just below Tortilla Creek. The river enters the reservoir through a gap near the lower end of the wide portion of the lake. The dam is 350 feet long and 229 feet high above bedrock, which lies about 70 feet below the bed of the river. It cost about $1,257,000, and the power plant, which develops 10,000 horsepower, an additional $500,000.

The Stewart Mountain Dam, holding the Sahuaro Reservoir, is 10 miles below the Mormon Flat Dam and 7 miles north of the Apache Trail, in a narrow part of the Salt River Canyon where the river passes though walls of granite. It is 210 feet high above bedrock and cost $2,300,000 for the dam and a power system of 17,500 horsepower. The storage capacity is about 70,000 acre-feet.

From Canyon Lake the road climbs rapidly to a divide consisting of the rhyolite tuffs and lavas of the volcanic succession, dipping north at moderate angles and showing many details of the relations of various lava flows and tuff accumulations. At many places the old Apache Indian trail is visible near the road. Not far beyond the summit in Apache Gap, Superstition Mountain comes into view, a huge pile of the same volcanic succession just crossed by the road but lying nearly horizontal and on a base of granite, which is revealed at a few points. (See p1. 31, B.) The precipitous west front of this mountain is skirted by the highway to and beyond the old Goldfield mining camp, which has produced considerable ore. Superstition Mountain is a famous subject for photographers and painters and probably appears in more pictures than any other mountain in the West. In the foreground are usually shown the sahuaro, cholla, and some other cacti and desert plants which are conspicuous in this region. A short distance north of Superstition Mountain and visible from points near Goldfield is Weavers Needle, a sharp peak of volcanic rock. In this vicinity was the Lost Dutchman mine, reported to have had wonderful richness. Many futile attempts have been made to find it.

PLATE 31.—A (top), BLOSSOMS OF PRICKLY PEAR CACTUS (NOPAL), SALT RIVER VALLEY NEAR PHOENIX, ARIZ. B (bottom), SUPERSTITION MOUNTAIN, ARIZ. From point near Apache Trail, 28 miles east of Phoenix, looking east. Ocotillo on right; giant cactus (sahuaro) in center, with cholla and other typical desert plants.

Five miles from Goldfield is Apache Junction, where the highway from Florence and Tucson joins the Apache Trail, and from this point a nearly due west course is taken to Phoenix. On the way are passed several hills and ridges, consisting of granite or schist, rising abruptly out of the desert, which here is a wide plain of alluvium irrigated by water from the Salt River.