WSP06362 - Laserfiche WebLink

Home Browse Search

Description moving generally eastward. These occur frequently from October to May, and seldom from June to September. The storms occur much more often in the northern part of the area than in the southern part. The eastern part of the Pacific Southwest is subject to convectional storms from the Gulf of Mexico which bring .sununer precipitation. The amount of precipitation during these storms tends to increase gradually, with altitude, on the western slopes of the mountain ranges, and decreases sharply on the eastern slopes. In summer, sufficient moisture and heat are present in the atmosphere to generate thunderstorms in much of the Pacific Southwest. Sununer precipita- tion is negligible in the coastal areas, but is about half the annual total in the southeastern portion of the Pacific Southwest. The mean annual precipitation for the area varies from about 2 inches in Death Valley in southern California to 120 inches on the western slopes ofthe Klamath Mountains near the California.Qregon border. Large sections of the area receive less than 10 inches of precipitation annually. Due to the small amount of sununer precipitation, successful agri. culture usually depends upon irrigation. SOCIAL ENVIRONS Early Settlement Present water resource development in the Pacific Southwest began with the early missionaries, settlers, and miners who diverted and used the supplies that were readily available. As population and the economy of the area increased, storage reservoirs, diversion dams, canals, wells, irrigation systems, municipal and industrial water distribution systems, and overland aqueducts were developed. The discovery of gold in California in 1848 gave a tremendous impetus to westward migration - a migration that continues to the present. Mining and agriculture developed rapidly in the decades following 1850. In some areas mining was first and stimulated agriculture and other support industries. However, mining followed agriculture in other locations, such as in Utah where Mormon pioneers established agricultural colonies as eariy as 1847. Copper mining began in the late 1800's; copper mines in Arizona, Nevada, Utah, and New Mexico now produce more than 85 percent of the Nation's total. Industrialization and the urbanization related to it became major factors during and after World War II. Growth and development are continuing along this trend. In 1965 the population of the Pacific South- west was 21.5 million. The 1970 census raises this amount to about 23.8 million, with 85 percent or more classified as urban. However, vast open spaces still remain, and the area has become well.known for its extensive scenic, wildlife, and recreational re- sources. Population and Employment Tables 2 and 3 present estimates of Pacific Southwest population and employment since 1940 and the percentage increase for each census period. On a percentage basis, both population and employ- ment grew at a rate more than double the Nation's rate of increase. Pacific Southwest population and employment, as a percentage of national population and employment, Table 2.-Population, 1940-1970 (Thousands olpersons) Region 1940 1950 1960 1965a 1970 California 6,948 10,678 15,765 18,106 20,136 Great Basin 592 742 985 1,151 1,216 Lower Colorado 582 869 1,505 1,877 2,156 Upper Colorado 272 281 338 337 345 Total: Pacific Southwest area 8,394 12,570 18,593 21,471 23,853 Pacific Southwest increase in % 49 48 15 11 United Statesb 132,594 152,271 180,684 194,592 203,874 Pacific Southwest % of United States 6.3 8.3 10.3 11.0 11.7 a 1965 estimated. b Includes armed forces overseas. 12