On Earth, cataracts represent regions where a river's gradient increases enough to create so much turbulence, that air gets incorporated into the water body forming a bubbly current sometimes called "whitewater". This image covers a location that may have acted as a cataract in the Kasei valley region. This observation from NASA Mars Reconnaissance Orbiter shows samples of bedrock lithologies which give us a measure of the post-flood erosion and modification history for the floor of Kasei Valles While there is a HiRISE stereo pair adjacent to this location that captures much of this cataract, it also misses some of the head scarp that might be the most useful, scientifically. http://photojournal.jpl.nasa.gov/catalog/PIA19351