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Changing Fish Fauna of the Southwest 369 s T white man (Olmstead, 1919, p. 9). As the river changed, it entrenched itself in its upper reaches and cut away much of the former flood plain, whereas in its lower course (below the mouth of the Santa Cruz River) the original well-marked channel soon became filled by flood deposits to form a broad, sandy plain (Bryan, 1925, pp. 342-343). In 1875, the well-defined channel of the Gila River near Solomonsville (in T. 7 S., R. 27 E.) had an average width of 138.6 feet and included an area of 103.57 acres, whereas by 1916 the same length of channel averaged more than 1,900 feet wide and occupied an area of 1,503 acres (Olm- stead,1919, p. 11). San Pedro River.-This stream (Fig. 1) was originally the only permanent southern tributary of the Gila River. In 1870 its nearly level valley had a narrow, grassy bed with banks that were well clothed with vegetation. There was an abundance of willow, cotton- wood, sycamore, and ash trees, with excellent growths of grasses (sacat6n and grama). Beaver dams retarded the heavy summer rains and prevented channel cutting. Cienegas, such as the one near the mouth of the then perennial Babocomari River (Dipeso, 1951, p. 3), were common. In the 1600'x, more than 2,000 aborigines lived in 15 villages along the lush San Pedro Valley below Fairbank (Dipeso; 1951, p. 7). By 1892 or 1893, however, a gully 3 to 20 feet deep had been cut for 125 miles, and by 1900, the river had entrenched its bed from 10 to 40 feet; trees and underbrush had been destroyed or greatly reduced, the grasses were largely gone, and cattle and horses, moving from feed to water, had cut numerous erosion channels from the hills to the river (Bryan, 1925, p. 342; Thornthwaite et al, 1942, p. 103). In its original condition, the San Pedro was of sufficient size and vol- ume to support a relatively large and varied fish fauna (Tab. II). San Simon Valley.-This valley is in southeastern Arizona and the adjacent part of New Mexico, and extends north-northwestward for 85 miles from the head of San Bernardino Valley (20 miles north of the International Line) to the Gila River at Solomon (formerly Solomonsville), just east of Safford. Tle often heavy summer storms were restrained in the valley by the extensive flats of sacat6n, and the water sank into the unbroken meadow to furnish an artesian supply near the central part of the valley. According to Olmstead (1919, p. 79) about 1883, "certain settlers near Solomonsville whose lands were along this drainage line were annoyed at finding occasionally after heavy rains that sand and detritus had been washed down on them