It, therefore, seems fortunate that the Coast Range is so placed as to intercept and concentrate a part of the moisture that the sea-winds carry, and doubly fortunate that its location is but a few miles from the coast, thereby giving temporary relief to the relatively crowded people of the lower irrigated valleys and the towns. The wet years formerly developed a crop of prospectors. Pack animals are cheaper when there is good pasture and they are also easier to maintain. So when the rains came the hopeful pick-and-shovel amateurs began to emigrate from the towns to search for ore among the discolored bands of rock intruded into the granite masses of the coastal hills. However, the most likely spots have been so thoroughly and so unsuccessfully prospected for many years that there is no longer any interest in the “mines.”
Transportation rates are still most intimately related to the rains. My guide had two prices—a high price if I proposed to enter a town at night and thus require him to buy expensive forage; a low price if I camped in the hills and reached the town in time for him to return to the hills with his animals. Inquiry showed that this was the regular custom. I also learned that in packing goods from one part of the coast to another forage must be carried in dry years or the beasts required to do without. In wet years by a very slight detour the packer has his beasts in good pasture that is free for all. The merchant who dispatches the goods may find his charges nearly doubled in extremely dry years. Goods are more expensive and there is a decreased consumption. The effects of the rains are thus transmitted from one to another, until at last nearly all the members of a community are bearing a share of the burdens imposed by drought. As always there are a few who prosper in spite of the ill wind. If the pastures fail, live stock must be sold and the dealers ship south to the nitrate ports or north to the large coast towns of Peru, where there is always a demand. Their business is most active when it is dry or rather at the beginning, of the dry period. Also if transport by land routes becomes too expensive the small traders turn to the sea routes and the carriers have an increased business. But so far as I have been able to learn, dry years favor only a few scattered individuals.
To the traveler on the west coast it is a source of constant surprise that the sky is so often overcast and the ports hidden by fog, while on every hand there are clear evidences of extreme aridity. Likewise it is often inquired why the sunsets there should be often so superlatively beautiful during the winter months when the coast is fog bound. Why a desert when the air is so humid? Why striking sunsets when so many of the days are marked by dull skies? As we have seen in the first part of this chapter, the big desert tracts lie east of the Coast Range, and there, excepting slight summer cloudiness, cloudless skies are the rule. The desert just back of the coast is in many parts of Peru only a narrow fringe of dry marine terraces quite unlike the real desert in type of weather and in resources. The fog bank overhanging it forms over the Humboldt Current which lies off shore; it drifts landward with the onshore wind; it forms over the upwelling cold water between the current and the shore; it gathers on the seaward slopes of the coastal hills as the inflowing air ascends them in its journey eastward. Sometimes it lies on the surface of the land and the water; more frequently it is some distance above them. On many parts of the coast its characteristic position is from 2,000 to 4,000 feet above sea level, descending at night nearly or quite to the surface, ascending by day and sometimes all but disappearing except as rain-clouds on the hills.[23] Upon the local behavior of the fog bank depends in large measure the local climate. A general description of the coastal climate will have many exceptions. The physical principles involved are, however, the same everywhere. I take for discussion therefore the case illustrated by [92] , since this also displays with reasonable fidelity the conditions along that part of the Peruvian coast between Camaná and Mollendo which lies in the field of work of the Yale Peruvian Expedition of 1911.
Three typical positions of the fog bank are shown in the figure, and a fourth—that in which the bank extends indefinitely westward—may be supplied by the imagination.
If the cloud bank be limited to C only the early morning hours at the port are cloudy. If it extend to B the sun is obscured until midday. If it reach as far west as A only a few late afternoon hours are sunny. Once in a while there is a sudden splash of rain—a few drops which astonish the traveler who looks out upon a parched landscape. The smaller drops are evaporated before reaching the earth. In spite of the ever-present threat of rain the coast is extremely arid. Though the vegetation appears to be dried and burned up, the air is humid and for months the sky may be overcast most of the time. So nicely are the rain-making conditions balanced that if one of our ordinary low-pressure areas, or so-called cyclonic storms, from the temperate zone were set in motion along the foot of the mountains, the resulting deluge would immediately lay the coast in ruins. The cane-thatched, mud-walled huts and houses would crumble in the heavy rain like a child’s sand pile before a rising sea; the alluvial valley land would be coated with infertile gravel; and mighty rivers of sand, now delicately poised on arid slopes, would inundate large tracts of fertile soil.
