Today's Image of Mars is from Kasei Valles, a 1780 km (1100 mi) long set of flood carved channels on Mars. This image focuses on a much narrower channel that was carved into Kasei Valles.
Many channels carved by water on Mars are covered by a more recent layer of lava. In many cases the fissures that released the water, later release the lava that covers the channels, but in the case of Kasei Valles, the lava came from a different location than the water.
Kasei Valles was carved by floods from Echus Chasma, but the lava came from a source between the Tharsis Volcanoes and only covers the lowlands of the valleys.
This image links to the original captioned image by HiRISE.