The effect of the last uplift of the coast was to impel the Majes River again to cut down its lower course nearly to sea level. The Pliocene terrace deposits are here entirely removed over an area several leagues wide. In their place an extensive delta and alluvial fan have been formed. At first the river undoubtedly cut down to base level at its mouth and deposited the cut material on the sea floor, now shoal, for a considerable distance from shore. We should still find the river in that position had other agents not intervened. But in the Pleistocene a great quantity of waste was swept into the Majes Valley, whereupon aggradation began; and in the middle and lower valley it has continued down to the present.
Fig. 150—Profile of the coastal terraces at Mollendo. At 1, in a tributary gorge, fossiliferous clay occurs at 800 feet elevation above the sea. At 2 is a characteristic change of profile marking a drop from a higher to a lower terrace. On the extreme left is the highest terrace, just under 1,500 feet (460 m.).