“Astronauts and their instructor take notes on their field observations during a geology training trip into the Grand Canyon, in Arizona. Although the rocks that are exposed at the Grand Canyon do not resemble lunar rocks in any way, the trip here was an important step in familiarizing the astronauts with the basics of geology, so that they could function well as observers and collectors.” Source: http://history.nasa.gov/SP-350/ch-7-8.html