NASA hopes Curiosity landing site is a Grand Canyon of Mars - Page 2 - latimes.com: Starting a couple of years ago, the MRO began sending home a data dump about the landing site finalists. The data made it clear that all of the finalists contained vast scientific possibilities, but none more than Gale Crater and its mountain.
The MRO was equipped with lasers that could peer into the planet's surface and detect the presence of minerals.
The mountain, it turned out, was once not a mountain at all. It was part of a giant, layered plateau, which was then eroded — perhaps by wind, perhaps by water — into a cone.
On its slopes, the MRO found distinct layers of rock, like those John Wesley Powell found in the Grand Canyon.