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

YUMA, ARIZ., TO SAN DIEGO, CALIF.

Sleeping cars from several trains continue westward from Yuma to San Diego over the San Diego & Arizona Railway, which is allied with the Southern Pacific lines. The distance is 218 miles, across Imperial Valley and the high sierra of southern California, with two long detours into Baja California. This railroad was completed in 1919 at a cost of $19,000,000. It has 22 tunnels, one of them about half a mile long.

The main line is left at Araz Junction, 6-1/2 miles west of Yuma, on Southern Pacific tracks extending to El Centro (40 miles). The railroad passes around the southeast end of the great belt of sand hills and looping into Mexico reaches Mexicali, Mexico, and the adjoining city of Calexico, Calif. El Centro is in the highly productive irrigated district of Imperial Valley. (See p. 248.) The New River, an old channel from the Colorado River, touched by the railroad at Calexico and crossed a short distance west of Seeley, occupies a trench in the desert plain much deepened and widened by the great flood of water that ran through it into Imperial Valley from the Colorado River in 1905. This stream ate deeply into the adjoining banks and damaged more than 7,000 acres of the adjacent region. The Alamo River, 10 miles east of El Centro, was another inlet for flood waters.

From Seeley westward there are fine views of Signal Mountain, a knob of old granite and schist not far away in Mexico, and of the Sierra de las Cocopas, consisting of volcanic rocks, which extend far to the south. Farther west is dimly outlined the high Sierra Pedro Martir (mar-teer'), in Baja California, which attains an elevation of more than 10,000 feet. It consists of light-colored granite. The northern extension of this range, known as the Laguna Mountains, is crossed by the railroad near Jacumba, about 50 miles farther on, where, however, the elevation is much less than in Mexico. The continuity of its steep eastern front, believed to be a fault scarp, is a striking feature for many miles. The West Line Canal, just east of Dixieland, separates the productive irrigated land, with its fine fields of cotton, alfalfa, barley, and maize, from the original desert, with its sparse vegetation of arid-land plants.

Just west of Dixieland sea level is reached on an up slope of the desert which continues westward to the foot of the mountains. Three miles west of Dixieland the beach of old Lake Cahuilla is crossed at about 40 feet above sea level. This lake occupied the Salton Basin sufficiently long to develop well-marked strand features. (See p. 253.) At Plaster City is a mill making plaster of paris from gypsum mined from large deposits in Fish Creek Mountain, 26 miles northwest, and brought by a branch railroad. The deposit is interbedded in strata of Tertiary age, and near by is a considerable body of the mineral celestite (strontium sulphate), also included in the sedimentary succession.

Halfway to Coyote Wells a low ridge is crossed showing tilted clay and sand of Tertiary age, truncated and capped by a thin mantle of sand and gravel. This ridge crosses the valley and rises into Coyote Mountain, which is conspicuous to the north. This mountain and Fish Creek Mountain, just beyond, consist mainly of a core of granite and marble and other metamorphic rocks, closely folded and encircled by Tertiary and later strata. The marble, which may be of Paleozoic age, is penetrated and metamorphosed by the granite. It is mostly of blue-gray color and has been quarried to a small extent at the east end of Coyote Mountain. Some portions contain considerable graphite in the form of carbon known as plumbago or black lead. A section through Coyote Mountain is shown in Figure 70.

FIGURE 70.—section across Coyote Mountain, Calif., near Alverson and Garnett Canyons. After Mendenhall. a, Limestone (Paleozoic) metamorphosed to marble by intrusive granite; b, sandstone and conglomerate; c, tuff (Miocene); d, shale (Miocene)

Lying on the metamorphic and intrusive rocks is a series of volcanic tuffs, agglomerates, and dark lavas which carry interbedded sandstones in Fish Creek Mountain. Upon these lie marine beds with corals and oyster reefs, containing many fossils. In Alverson Canyon on the south side of Coyote Mountain, red vesicular lava is overlain by green and lavender sandstones and conglomerate containing much volcanic matter, in all from 100 to 200 feet thick. Next above are tawny sandstones and a thick succession of soft greenish-yellow shale or clay which forms conspicuous badlands in the slopes between Carrizo Mountain and Fish Creek Mountain. High-level terrace deposits lie across the planed-off edges of the shale. The Tertiary beds and their fossils have been described by Mendenhall, Kew, T. W. Vaughan, and Woodring.

Tertiary beds also constitute the Yuha Buttes, 8 miles west of Dixieland. Among many fossils occurring in the sandstones on these mountains are numerous corals, many of them finely preserved. According to Vaughan, this coral fauna, which is considered to be of early Pliocene age, contains forms not found in the Pacific Ocean. Its Atlantic Ocean affinities indicate that in late Tertiary time there was an oceanic connection that permitted the Atlantic fauna to extend to the head of the Gulf of California; this connection, however, may have been as far south as the Isthmus of Tehuantepec. Fossils, especially scallop shells, occur in large numbers about Carrizo Mountain and near Yuha Wells, 6 miles southwest of Dixieland.

West of Coyote Wells and extending far south and north is the steep east front of the Laguna Mountains, which form the extension of the Sierra Pedro Martir of Baja California. The range presents cliffs and rugged slopes of white granite, which are climbed by the picturesque main highway to San Diego, an ascent of more than 2,500 feet, passing through Mountain Springs at the foot of the mountains and Jacumba Springs near the top. At the foot of this slope in places are hills of old gravel and boulder deposits rising considerably above the main valley slope and capped by lavas. The railroad ascends the valley and near Dos Cabezas siding reaches the base of the Laguna Mountains, in which are exposed marble and schist apparently underlying the great mass of granite which rises so abruptly to the westward. A mile beyond Dos Cabezas foothills of granite are entered and the low divide into Carrizo Valley is crossed. Thence the railroad swings southward and ascends this valley and the deep Carrizo Gorge, at its head. The gorge is about 11 miles long, and there are many deep cuts, tunnels, and long shelves cut on the precipitous slopes, in places 900 feet above the creek. The scenery is remarkably impressive. The rock is mostly a massive light-colored granite, sculptured into many picturesque forms in the steep canyon walls. (See pl. 49.) The effects of jointing and erosion are well shown. It is believed that this valley is developed along a fault. Carrizo is the local name for the grass growing in the depths of the gorge and used by the Indians in basket making. Palms also grow in several places near the stream bed.

PLATE 49.—CARRIZO GORGE, ON ROUTE FROM YUMA, ARIZ., TO SAN DIEGO, CALIF. From painting by W. H. Bull.

At the head of the deep canyon the railroad comes out into a park which extends about 3 miles to Jacumba Springs. This park is due to a dropped block of lava on tuffs (Tertiary) which caps the granite in an area of several square miles in this region. The sketch section in Figure 71 shows some of the features.

FIGURE 71.—Section about 2 miles north of Jacumba Springs, Calif.

At Jacumba Springs (elevation 2,830 feet), where the granite appears again, there are warm springs with faint sulphureted hydrogen emanation and notable mineral contents. Here a resort has been developed. The water was used by Indians and early aborigines, who have left many traces of their presence. North of Jacumba there is a belt of schists, slates, and other metamorphic rocks which are regarded as Paleozoic. West of Jacumba there is a long ascent up the granite slope to the summit at Hipass (elevation 3,660 feet). In this region the granite is weathered into many grotesque forms, mostly rounded, with numerous balanced rocks and rugged pinnacles. Pronounced jointing has had much to do with the development of these features. The granite of the entire range is mostly light colored, of uniform grain, and very massive, so that much of it would make a fine building stone. It is cut by dikes of darker rocks, and there are zones in which the jointing is closely spaced and the rock considerably shattered.

The mountain vegetation is very different from that of the desert, with much manzanita and live oak. The manzanita (Arctostaphylos patula) is a shrub having a smooth bark of rich chocolate-brown color, small pale-green roundish leaves, and berries that resemble diminutive apples. It is this resemblance that gives the shrub its common name, which in Spanish signifies little apple. Bears are very fond of these berries. The manzanita covers many of the hills in California with a stiff, almost impenetrable growth. Its wood is hard, and the blaze from an old gnarled root cheers many a western fireplace. The live oak grows generally in the valleys, for the mountains are mostly covered by bushes with many bare rocky spots. The summit is broad and rolling, with parks at intervals. The country near the pass is not high enough for pine, which occurs on the adjoining highlands. On the west side of the pass the railroad makes a long tortuous descent through the Campo Indian Reservation into the valley of Campo Creek, which is followed to a point considerably below Campo.

Campo is a small settlement in a parklike valley surrounded by granite hills on which are many great residual boulders of granite. This granite is the source of fine gems at various places in San Diego County, notably tourmalines of red, green, and pink colors. A rare form of spodumene known as kunzite occurs in crystals of beautiful purple and violet tints. Garnets and beryls are also obtained, and some of the beryls are white or pale rose and almost as brilliant as diamonds.

Between Campo, Calf., and Tecate, Mexico, the international boundary line is crossed in tunnel 4, the deflection into Mexico being required to obtain a suitable grade for the railroad on the west side of the mountain. For the next 43 miles the track follows the northern margin of Baja California. A long descent is made in a great S-shaped course to Redondo, a small village in a wide granite valley with high ridges on all sides. This valley is followed to the west, finally down a deep gorge in porphyry (beyond Matanuco) which leads out into the coastal plain of the west coast of California. This plain is a smooth high terrace of gravel and sand (Pleistocene or late Tertiary), deeply trenched by the valley of Tia Juana Creek (tee'a wah'na, Spanish for Aunt Jane), which the railroad follows to the city of Tia Juana. Two miles east of the city it passes the picturesque resort of Agua Caliente, with casino, hotel, race course, and other features, where annual handicap horse races and golf tournaments are held.

From Tia Juana the railroad turns north into the United States and, crossing a low coastal terrace plain, reaches San Diego in a distance of 16 miles.

The beautiful city of San Diego has developed about a fine harbor in the southwest corner of California. The mild winter climate and temperate summers have had much to do with attracting a large population. The harbor was discovered by the Portuguese navigator, Juan Rodríguez Cabrillo, in September, 1542, and was named in 1602 by Don Sebastián Vizcaino, a Spanish explorer. The first mission in California was the Mission San Diego de Alcalá, founded at a small Indian ranchería (site of present Old Town) by Padre Junípero Serra in July, 1769; it was moved to the present location in 1774. Destroyed Without warning by the Indians in 1775, it was reestablished in 1776 and flourished until secularized in 1834. Mexican administration of the settlement was organized in 1822. The city is built on marine plains and terraces which slope seaward from the Cuyamaca Mountains (coo-ya-mah'ca) on the east and the Ysidro Mountains (ee-see'dro) to the south. The harbor is used by many large ocean vessels, and along its margin are the United States Naval Station, Fort Rosecrans, and the Army and Navy aviation headquarters. Many fine beaches, notably Coronado, with its tent city and hotel, and Mission Beach, attract large numbers of visitors. Balboa Park, 1,400 acres in extent and of great beauty, contains museums of natural history and art, housed in some of the handsome buildings built for the exposition of 1915. At Old Town, on the north edge of the city, are the old mission, old Fort Stockton, the monument where in 1846 General Frémont first planted the United States flag, and the marriage place of Helen Hunt Jackson's "Ramona."

The Point Loma peninsula, which separates the ocean from the bay, is a residential section and the headquarters of the Theosophical Society. This peninsula is underlain by soft shales and sandstones, carrying fossils of Chico (Upper Cretaceous) age capped by cliff-making conglomerates of late Tertiary age and to the north passing under sandstones carrying Eocene fossils. The famous sea cliffs of La Jolla (hoe'ya) are 14 miles north, and near them is the Scripps Institution of Oceanography of the University of California. In these cliffs and adjacent areas Cretaceous and Eocene strata are exposed.

The temperature of the San Diego region is very rarely below 32° or above 90°. Myriads of flowers and abundant shade trees are notable features. Oranges, lemons, and other fruits, besides vegetables in great variety, are grown in the adjoining region. One large industry at San Diego is milling lumber brought down the coast from Oregon in huge rafts.