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i Changing Fish Fauna of the Southwest 371 ton-wood trees ... the river-bottom is in some places marshy, with willow thickets, and in others covered with a loose, pulverized soil." In the 1880's the river, shortly above Grand Falls (about 35 miles northeast of Flagstaff), was a narrow perennial stream, and its banks were bordered by a fine stand of old and young cottonwoods. Many beavers were supported by an ample food supply in the young cotton- wood trees. Grama grass covered the adjacent hills. Today, the Little Colorado is normally dry between Grand Falls and Winslow, the trees have long since disappeared, and the fine grass has vanished. When the river does flow between Holbrook and Winslow, it is through a wide, treeless valley, where its bed is broad and sandy, its banks deeply entrenched, and vegetation is scarce. Since around the turn of the century, disastrous floods have converted its sandy bed into a raging, eroding torrent, heavily laden with silt. oTHM AWAS Southern California. The major coastal valley is a complex lowland that lies at the southern base of the San Gabriel and San Bernardino ranges, opens directly westward to the Pacific, and com- municates with the Mohave and Colorado deserts via Cajon and San Gorgonio passes. Its total area is about 3,000 square miles. Three major streams traverse this valley, herein called the Los Angeles Plain: the Santa Ana, the San Gabriel, and the Los Angeles. Of these, the Santa Ana River is the largest. It rises high in the San Bernardino Mountains and flows to the Pacific through 2 canyons on the plains, ai, upper (about 50 miles west of its source) and a lower (through the Sara Ana Moun, is) ; its total length is about 100 miles. The utili: ation of this r er by man is indicated by the following state- ment: "Probably nc other stream of its size in the United States is made to serve greater or more varied uses" (McGlashan,1930, p. 176). West of the Santa Ana is the San Gabriel River, with a total length of about 70 miles; its headwaters rise on the western flank of Mount San Antonio (Old Baldy) and from the southern slopes of other high peaks. The Los Angeles River originates to the northwest of the city in several small tributaries which normally sink into the sands of San Fernando Valley. Impervious rocks at the lower end of this valley force the underground water to the surface, and the river originally flowed from this point through a valley of low, rolling hills to the •