The pampa surfaces are inclined in general toward the sea. They were built up to their present level chiefly by mountain streams before the present deep valleys were cut, that is to say, when the land was more than a half-mile lower. Some of their material is wind-blown and on the walls of the valleys are alternating belts of wind-blown and water-laid strata from one hundred to four hundred feet thick as if in past ages long dry and long wet periods had succeeded each other. The wind has blown sand and dust from the desert down into the valleys, but its chief work has been to drive the lighter desert waste up partly into the mountains and along their margins, partly so high as to carry it into the realm of the lofty terrestrial winds, whence it falls upon surfaces far distant from the fields of origin. There are left behind the heavier sand which the wind rolls along on the surfaces and builds into crescentic dunes called médanos, and the pebbles that it can sandpaper but cannot remove bodily. Thus there are belts of dunes, belts of irregular sand drifts, and belts of true desert “pavement” (a residual mantle of faceted pebbles and irregular stones).
Yet another feature of the desert pampa are the “dry” valleys that join the through-flowing streams at irregular intervals, as shown in the accompanying regional diagram. If one follow a dry valley to its head he will find there a set of broad and shallow tributaries. Sand drifts may clog them and appear to indicate that water no longer flows through them. They are often referred to by unscientific travelers as evidences of a recent change of climate. I had once the unusual opportunity (in the mountains of Chile) of seeing freshly fallen snow melted rapidly and thus turned suddenly into the streams. In 1911 this happened also at San Pedro de Atacama, northern Chile, right in the desert at 8,000 feet (2,440 m.) elevation, and in both places the dry, sand-choked valleys were cleaned out and definite channels reëstablished. From a large number of facts like these we know that the dry valleys represent the work of the infrequent rains. No desert is absolutely rainless, although until recently it was the fashion to say so. Naturally the wind, which works incessantly, partly offsets the work of the water. Yet the wind can make but little impression upon the general outlines of the dry valleys. They remain under the dominance of the irregular rains. These come sometimes at intervals of three or four years, again at intervals of ten to fifteen years, and some parts of the desert have probably been rainless for a hundred years. Some specific cases are discussed in the chapter on Climate.
The large valleys of the desert zone have been cut by snow-fed streams and then partly filled again so that deep waste lies on their floors and abuts with remarkable sharpness against the bordering cliffs ([Fig. 155]). Extensive flats are thus available for easy cultivation, and the through-flowing streams furnish abundant water to the irrigating canals. The alluvial floor begins almost at the foot of the steep western slope of the lava plateau, but it is there stony and coarse—hence Chuquibamba, or plain of stones (chuqui = stone; bamba = plain). Farther down and about half-way between Chuquibamba and Aplao (Camaná Quadrangle) it is partly covered with fresh mud and sand flows from the bordering valley walls and the stream is intrenched two hundred feet. A few miles above Aplao the stream emerges from its narrow gorge and thenceforth flows on the surface of the alluvium right to the sea. Narrow places occur between Cantas and Aplao, where there is a projection of old and hard quartzitic rock, and again above Camaná, where the stream cuts straight across the granite axis of the Coast Range. Elsewhere the rock is either a softer sandstone or still unindurated sands and gravels, as at the top of the desert series of strata that are exposed on the valley wall. The changing width of the valley is thus a reflection of the changing hardness of the rock.
There is a wide range of products between Chuquibamba at 10,000 feet (3,050 m.) at the head of the valley and Camaná near the valley mouth. At the higher levels fruit will not grow—only alfalfa, potatoes, and barley. A thousand feet below Chuquibamba fruit trees appear. Then follows a barren stretch where there are mud flows and where the river is intrenched. Below this there is a wonderful change in climate and products. The elevation falls off 4,000 feet and the first cultivated patches below the middle unfavorable section are covered with grape vines. Here at 3,000 feet (900 m.) elevation above the sea begin the famous vineyards of the Majes Valley, which support a wine industry that dates back to the sixteenth century. Some of the huge buried earthenware jars for curing the wine at Hacienda Cantas were made in the reign of Philip II.
The people of Aplao and Camaná are among the most hospitable and energetic in Peru, as if these qualities were but the reflection of the bounty of nature. Nowhere could I see evidences of crowding or of the degeneracy or poverty that is so often associated with desert people. Water is always plentiful; sometimes indeed too plentiful, for floods and changes in the bed of the river are responsible for the loss of a good deal of land. This abundance of water means that both the small and the large landowners receive enough. There are none of the troublesome official regulations, as in the poorer valleys with their inevitable favoritism or downright graft. Yet even here the valley is not fully occupied; at many places more land could be put under cultivation. The Belaunde brothers at Cantas have illustrated this in their new cotton plantation, where clearings and new canals have turned into cultivated fields tracts long covered with brush.
The Majes Valley sorely lacks an adequate port. Its cotton, sugar, and wine must now be shipped to Camaná and thence to Mollendo, either by a small bi-weekly boat, or by pack-train over the coast trail to Quilca, where ocean steamers call. This is so roundabout a way that the planters of the mid-valley section and the farmers of the valley head now export their products over the desert trail from Cantas to Vitor on the Mollendo-Arequipa railroad, whence they can be sent either to the cotton mills or the stores of Arequipa, the chief distributing market of southern Peru, or to the ocean port.
The foreshore at Camaná is low and marshy where the salt water covers the outer edge of the delta. In the hollow between two headlands a broad alluvial plain has been formed, through which the shallow river now discharges. Hence the natural indentation has been filled up and the river shoaled. To these disadvantages must be added a third, the shoaling of the sea bottom, which compels ships to anchor far off shore. Such shoals are so rare on this dry and almost riverless coast as to be a menace to navigation. The steamer Tucapelle, like all west-coast boats, was sailing close to the unlighted shore on a very dark night in April, 1911, when the usual fog came on. She struck the reef just off Camaná. Half of her passengers perished in trying to get through the tremendous surf that broke over the bar. The most practicable scheme for the development of the port would seem to be a floating dock and tower anchored out of reach of the surf, and connected by cable with a railway on shore. Harbor works would be extraordinarily expensive. The valley can support only a modest project.