Those guys with the "Dirt For Sale" signs on the side of the road may be in on a secret the rest of us don't know about. Events such as Monster Jam monster truck rallies and the AMP'D MOBILE SUPERCROSS SERIES use an ungodly amount of the stuff. The Sat., FEB. 24, SX (supercross abbreviation for those in the know) race needs roughly 1.5 billion pounds, but only seven dudes with bulldozers to smooth and shape it into a grit-filled dirt-bike obstacle course. The world's top riders, including Ricky Carmichael, Chad Reed and James Stewart (right), race this weekend at speeds upward of 60 mph and heights capable of clearing a three-story building. $10-$47. Practice/qualifying: 12:30 p.m. Race: 7 p.m. Georgia Dome, 1 Georgia Dome Drive. 404-249-6400. www.supercrossonline.com.