The valley networks on Mars are terrains eroded by flowing water billions of years ago.
In places where the bedrock is well exposed, we often see a variety of colors due to altered minerals and polygonal patterns perhaps due to wet, clay-rich deposits.
Written by: Alfred McEwen (audio: Tre Gibbs) (18 May 2016)
More info and image formats at http://hirise.lpl.arizona.edu/ESP_045299_1545
Image: NASA/JPL/University of Arizona