The rovers deployed to Mars are able to drill down into the surface, but only some centimeters, and so it's been difficult to get a picture of the geology of Mars in fine detail.
As Wired writes:
Fortunately, land erodes. Forget radar and drilling robots: Locate a spot of land laid bare by time, and you have a direct line of sight on Mars' subterranean layers—and any ice deposited there.
Now, scientists have discovered such a site. In fact, with the help of HiRISE, a powerful camera aboard NASA's Mars Reconnaissance Orbiter, they've found several.
This is a very exciting find for anybody hoping to establish a civilization on Mars. Something of a long shot, and I think we'll have to develop Asteroid Mining in order to setup adequate interplanetary infrastructure in order to support any large colony on Mars.
But, with this news, at least they should be some easily accessible (and relatively clean) sources of water - a crucial component of life as we know it.
