NASA’s Perseverance Mars rover took this selfie on September 10, 2021. NASA/JPL-Caltech/MSSS NASA's Perseverance rover on Mars snapped photos of cliffs that show signs of ancient flash floods. The first study of Perseverance's data suggests that a flooding river dragged boulders for miles. The photos also pinpoint ancient river sediment in which the rover could search for fossilized life. In the dry Martian crater where NASA's Perseverance rover is searching for signs of long-gone life, torrential flash floods once dragged boulders for miles.That's what researchers concluded in the first study of Perseverance's data since the rover landed on Mars in February.Its landing site, a 28-mile-wide crater called Jezero, was filled with water more than 3.5 billion years ago.