To re-create a sea of craters like what the astronauts would encounter on the moon, scientists in 1965 dug more than 400 holes. They calculated exactly how much dynamite and nitrate fertilizer to cram into the earth to create different-sized craters.The area surrounding Flagstaff was the perfect location to re-create the moon's surface, says the narrator in one of the U.S. Geological Survey's movies from the 1960s. "Near Flagstaff, Ariz., are fields of volcanic cinders, the result of eruptions about the year 1065. The cinders provided excellent material to re-create the lunar surface."The result of this was an accurate replica of a section of the moon's Sea of Tranquility, where Apollo 11 landed. Today, the crater field is a playground for motorbikes and ATVs. They kick up clouds of cinders as they cruise in and out of the craters. Forty years ago, NASA asked scientists in Flagstaff to build an early predecessor of these off-road vehicles — a replica of the lunar rover for astronauts to train on.