Canyon Walls -- Earth and Moon
Layered igneous bedrock is visible along the upper 60 m of Hadley Rille (left) which is believed to be a collapsed lava tube or channel about 3.3 billion years (b.y.) in age. Because of its similar dimensions and bedrock, the Rio Grande Gorge, New Mexico, was chosen as the training site for Apollo 15 astronauts. The steep-walled canyon (right) exposes a cross section of a volcano-covered plateau; the Servilleta basalt is nearly identical to basalts of the ocean floor (3.6 to 4.5 million years old).
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