8 



Usinger: Introduction 



San Gorgonio Pass present Chocolate Mlns. 



Colorado River 



Colorado River 

 Silt Dam 



Intro, fig. 11. Diagrammatic representati 

 (reprinted from Sunset Magazine, Febroar 



and biotic evidence. The principal topographic and 

 aquatic features of the state are shown on the accom- 

 panying relief map (intro. fig. 12). Essential features, 

 from the viewpoint of an aquatic biologist, are the high 

 mountain ranges surrounding the Central Valley, 

 with drainage through the Carquinez Straits to San 

 Francisco Bay; the coastal slopes on the west; and 

 the southern California deserts with isolated mountain 

 ranges. Faunistically, the picture is, of course, 

 very complex, but certain broad generalizations have 

 crystallized out of recent analyses of the best-known 

 group of animals — the birds (Miller, 1951) (intro. fig. 

 13). In general, the pattern derived from birds can be 

 applied directly to aquatic insects, the minor devia- 

 tions being attributable to the special nature of 

 aquatic habitats. 



The dominant fauna of the northern part of Calif- 

 ornia and of the higher mountains in the south is 

 boreal. This includes the barren alpine regions and 

 the evergreen coniferous forests. It is similar to, 

 and more or less continuous with, the widespread 

 coniferous forests of northern North America and of 

 the Rocky Mountains. Minor differences in California 



are due to the heavy snow pack in the winter and 

 the virtual lack of summer rains with consequent 

 arid conditions, especially in the south. 



Intruding from the east are the Great Basin faunal 

 elements, with important sections in Modoc and Lassen 

 counties, along the desert slopes of the Sierra, and 

 in the Owens Valley and Mojave Desert. A striking 

 feature of this region is the relict southern fauna of 

 the hot springs of Death Valley and adjacent parts 

 of Nevada in the Amargosa River system. 



Southern elements in the aquatic fauna are now 

 confined (except for the Death Valley relicts) to the 

 Colorado drainage system. The Colorado River itself, 

 with its oxbows, sloughs, and reservoirs, is a rich 

 source of Sonoran and Neotropical types, and streams 

 on the California side are strictly comparable to 

 those of the nearby Gila Mountains in Arizona. 



The rest of the state, including the Central Valley, 

 the south and central Coast Range, and the western 

 foothills of the Sierra can best be called Californian. 

 It is a region of winter rains and summer drought. It 

 is not rich in aquatics but, because of its isolation 

 and presumably also its age, is unique in character. 



