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<br />. <br /> <br />II. A GENERAL DESCRIPTION OF THE PROJECT AREA <br /> <br />. <br /> <br />The overall project area is located in southwestern Arizona (YlIma and Maricopa <br />Counties) and the northwest tip of Sonora. Mexico (between the Southerly International <br />Boundary and the Gulf of California). on tile historic 1100d pbin and delta of the Lower <br />Colorado and Gila Rivers. The focal point of the project. however. is a much smaller <br />area centered uround YlIllla, ArizoJ1a~ along thl.:' Gil:.J. Riv\..'r from T l'XilS Hill west to the <br />Colorado River, and from Impl'ri.Ji D"m south to San Luis (M"p No. X-300-701). All <br />structural features and llonstructl1r~ll rnt'~ISLlrl'S, \,,'ith the exception of Painted Rock Dam <br />'Ind the Bypass Dr"in-Mexil.o. are or will be located within this smaller area. generally <br />rt't'L'rrt:'d to us the YUllla ~lrt",l. <br />A. PhysiL.'~l1 CI1Jr:.H.:krist ics <br />[aell or tilt' project art'<J IS various physical characteristics differs from ont' isolatt'd <br />or unique IOL';lIt" to .lllother witlIin tht' overall area, but thL'SL' individual c1wr<1cteristics <br />bener"lly tvpify the I'hysiogrolphy and physiology of the Sonoran Desert. Several of these <br />ch~lr:lct('risllcs-~topogr.lpl1y. soils. ;lnd agricultural vt=get~ltion--pertain only to the YUllla area. <br />whlk' otl1l'rs dre reprl'sentJtivt' of the entire project area. <br />A.I. Climate <br />The rl'gion~lI dilllate. typical of the (ksL'rt environment. is hot <lnd dry. The <br /><lv\.'r..lg.\..' lllaxilllUlll temperature from June tllrough August is I060F ami the average <br />1ll1l1illltlm tL'llllWflJture in Jalllltlry is 40oF. This l~xt('nt of warm wt'[ttl1t.'r results in ,.I frost-fret' <br />period whiL'h .lver:.Igl'S 348 days a year. Annual precipitation averages 3 inches in the Yum~l <br />arl'iJ. HIlLI Ol'CUrs:.lS bril'f rains during a prill1:.Jry period from July to October and a secondary <br />pl'riod during the winter. HL'avy general precipitation may take place in late SlIllllller with <br />till' arrival of tropical air from off the west (oast of Mexico. but slIch storms Ol'ClIr on <br />,.Ill avc:-r:.Jgl' of only ollce every 7 years in the delta rL'gion. The predominant wind direction <br />is from the south during the warmer I"lrt of the year (June through August) and from <br />the north during the colder 1110nth, (November through February>. <br />A.2. Topography and Soils <br />The terrain of the Yuma area is l.llHracterized by !lood plains and terraces crossed <br />by arroyos and separated into valleys by low. rugged hills :.ltHJ lllountains oriented in a <br /> <br />northwl~st-solltheast direction. <br /> <br />. <br /> <br />10 <br />