A dust storm known as a haboob hit the Phoenix, Arizona area on Tuesday night, July 5, 2011.
Arizona State has a good page on basics of Arizona summer weather, including a discussion of a haboob - a lens-shaped dust cloud associated with a gust front from a thunderstorm.
The Arizona Republic story on the day after has a good map, showing the spread of the dust storm throughout the southwestern corner of Arizona including Tucson, Yuma, and Phoenix.
The Tuscon Citizen review in their Wry Heat column by Jonathan DuHamel includes after-incident reports from the National Weather Service and Accuweather. "The storm traveled at least 150 miles, much farther than the average 25 to 50 miles that dust storms typically travel."