The U.S. Department of Agriculture's National Agricultural Statistics Service (NASS) released "new satellite images depicting agricultural land cover across most of the nation for the 2009 crop year. The images, referred to as cropland data layers (CDL), are a useful tool for monitoring crop rotation patterns, land use changes, water resources and carbon emissions."
The Western US layer, covering Arizona and adjacent states, is a 47 Mb download.
NASS produced the CDLs using satellite images observed at 56-meter (0.775 acres per pixel) resolution and collected from the Resourcesat-1 Advanced Wide Field Sensor (AWiFS), Landsat Thematic Mapper and Moderate Resolution Imaging Spectroradiometer (MODIS).
[taken in part from the NASS news release]