Step through the Cinder Lake Crater Field roughly 12 miles outside Flagstaff, Ariz., and you might encounter a white crystal-filled rock that has absolutely no business being there.
The chunks of anorthosite weren't deposited there by nature -- they were trucked in from the mountains around Pasadena. And the craters were carved not by meteors, but by fertilizer and dynamite.
Before the first man landed on the moon, NASA dispatched the Apollo astronauts to this volcanic field to search for these and other faux moon rocks.
The scavenger hunt had great purpose: Anorthosite would likely be among the oldest lunar fragments, geologists believed, and they wanted to make sure the moonwalkers could identify the valuable specimens to bring home.
"We drilled that into the Apollo 15 crew," said Gerald Schaber, a retired geologist with the U.S. Geological Survey who helped with the training. "That's the kind of efforts we went to."
The early Apollo missions were focused on beating the Soviets to the moon to prove America's technological superiority during a fraught period in the Cold War, and the astronauts who flew them were mostly pilots with little interest in rocks.
But by the time Apollo 11 blasted off, many astronauts had come to develop an appreciation for lunar geology -- and the new light it would shed on our own planet.
"Geology opened my eyes to the immensity of time," Edwin "Buzz" Aldrin wrote in his 1973 book, "Return to Earth."
Northern Arizona became the hub of this crash course in field geology thanks in part to Meteor Crater, a nearly mile-wide wound in the desert less than 40 miles east of Flagstaff.
The crater caught the eye of USGS geologist Eugene Shoemaker, who dreamed of going to the moon but was disqualified by a diagnosis of Addison's disease, an adrenal gland disorder. Instead, he did his best to turn NASA's astronauts into scientists and persuaded the space agency to send nine of them to Arizona for field training.