 One such environment is at the Yuma Proving Grounds, a desert area where an existing Unexploded Ordnance (UXO) test site, the Steel Crater Test Area, has been used for a variety of sensor calibrations.It contains buried land mines, wires, pipes, vehicles, 55-gallon drums, storage containers and arms caches.For the Army studies to define the signatures of UXO detection, over 600 additional pieces of inert UXO were added to the Steel Crater Test Area, including bombs (250, 500, 750, 1000, and 2000 lb), mortars (60 and 81 mm), artillery shells (105 and 155 mm), 2.75-in.