Juventae Chasma's Gypsum Hills
On the north side of Mars' great equatorial rift Valles Marineris lies a large depression called Juventae Chasma. Juventae stretches for 180 kilometers (110 miles) east-west and 250 km (155 mi) north-south. Most of its floor lies 5,000 meters (16,000 feet) or more below the surrounding surface. It's a big hole in the ground.
In ages past, this big hole also held a lot of water. Three to four billion years ago, deep pools of water in Juventae Chasma created large deposits of clays, plus gypsum and other sulfate minerals.
Today, only relic hills and ridges remain of these deposits. But as testimony to an ancient wet period that may have seen life on Mars, the layered hills on Juventae's floor are drawing much scientific interest.