Before landing on the surface of the moon in 1969, astronauts Neil Armstrong and Buzz Aldrin needed a training ground that matched their destination’s cratered surface.

In the U.S., that turned out to be northern Arizona.

Starting in 1967, the U.S. Geological Survey used hundreds of pounds dynamite to blast holes into the surface of ancient lava fields south of Sunset Crater, near Flagstaff.

The first Cinder Lake crater field was designed to mimic the Sea of Tranquility, the lunar surface on which the astronauts would land. The craters in this 1968 image have eroded in the decades since then, but their outlines are still visible in 2017.

A second crater field was created in July of 1968. Its 380 craters have also lost contours to time, but the pockmarks are still apparent in aerial shots of the area, which is now used by off-road vehicles.

Apollo astronauts would continue to train in the Flagstaff area for years after the first moon landing.