Hypanis Vallis is a 270 km valley in Xanthe Terra on Mars at 11ºN, 314ºE. It appears to have been carved by long-lived flowing water, and a significant river delta exists at its outlet into the lowlands.
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Hypanis Vallis, as seen by HiRISE. Scale bar is 500 meters long.
Read more about Hypanis Vallis: Mars Science Laboratory