The Colorado River is the principal source of water for irrigation and domestic use in Arizona, southern California, and southern Nevada. To account for water use by each State and individual user, and to verify fallowed lands for conservation programs and other water management analyses, the Bureau of Reclamation routinely monitors more than 3.5 million acres of agriculture and riparian vegetation along the Lower Colorado River from Hoover Dam south to the international border with Mexico. Multispectral satellite images are analyzed in combination with other spatial data in a geographic information systems (GIS ) environment to generate information regarding crop and riparian types, acreages, and associated water use estimates. This information assists the BOR in fulfilling its U.S. Supreme Court mandate to provide detailed and accurate records of diversions, return flows, and consumptive use estimates of water diverted from the main stream of the Lower Colorado River. This program is an example of implementing methodologies based on remote sensing to routinely meet BOR water management analysis needs.
http://www.usbr.gov/lc/region/g4000/wtracct.html
Winter crop classification, Yuma area, AZ (imagery courtesy of Esri image services). North is oriented toward the top of the image.