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<br />cr:. <br />~ <br />c <br />r:- <br /> <br />:~iJ~ <br /> <br />PART II <br />BACKGROUND INFORMATION <br /> <br />Description of Affected Area <br /> <br />Most of the Colorado River Basin below Hoover Dam is desert. <br />Downstream from Lake Mead and Hoover Dam, the river passes through <br />narrow canyons and broad valleys, except in the south near Yuma <br />where a substantial broadening of the valley occurs. (See page 6 <br />for a map of affected area.) <br /> <br />The climate of the Lower Colorado River basin is notable for <br />lack of precipitation and high summer temperatures, routinely <br />exceeding IOoof. Temperatures above 1200f have been recorded <br />in the lower basin. Mean annual precipitation ranges from less <br />than 3.5 inches per year in Yuma to about 6 inches per year <br />near Hoover Dam. <br /> <br />The Lower Colorado River basin contains a variety of natural <br />vegetation. Three different and distinct deserts---the Mohave, <br />Western Sonora, and Eastern Sonora---merge in the floodplain. <br /> <br />Wildlife of the Lower Colorado River basin is as diverse as <br />its vegetation, due in part to the influence of the river. <br />Without the river, the wildlife community would be limited to <br />those species that can survive in a harsh desert atmosphere of <br />searing temperatures and desiccating climate. <br /> <br />Principal natural resources of the Lower Colorado River flood- <br />plain utilized by man are soil, water and. climate. Through <br />countless years of untamed flooding and meandering, the Colorado <br />River and its major tributaries laid down broad plains of fertile <br />alluvial soils in the deserts of California and Arizona. Today, <br />these rivers are extensively controlled and provide vital irri- <br />gation water supporting a vast agricultural industry. Waters of <br />the Lower Colorado are further used to produce hydropower and <br />support urban populations in Los Angeles, San Diego City and, <br />soon, Phoenix, Arizona. Recreational water sports .and attendant <br />commercial establishments directly dependent on Colorado River <br />water rival agriculture in economic importance. <br /> <br />Generally, economic development in the affected area is oriented <br />to the river and falls into four main categories: agriculture, <br />recreation, tourism and retirement. These exist in various <br />combinations in the flood impact area, with some aspects of <br />each present in all reaches. Agricultural use is primarily <br />on the Indian reservations in the Palo verde Valley (Blythe) <br />and in the floodplain area of Yuma. The Parker Strip (between <br />Parker Dam and the town of Parker) is an intensively developed <br />recreational area. Many, if not most, of the residences along <br />the. Strip are either retirement or vacation homes. <br /> <br />The lower Colorado River is also an important source of munic- <br /> <br />7 <br />