This is an image of a Martian river valley.
Click on image for full size
Image from: NASA
Martian River Valley Networks
Unlike the Martian outflow channels, these Martian river valleys exhibit many tributaries.
These river valleys do not resemble their terrestrial counterparts either, however. The tributaries are very short, on the order of 100m (the length of a football field), as if the running water ran out quickly.
One explanation for these is that they formed from melting ground ice. The ground ice could have melted either from a global warming episode, a local warming episode due to volcanic activity, or from hydrothermal activity, where water circulating underground affected the surface. (Evidence of hydrothermal activity has implications for life on Mars.)
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