Hebrus Valles is an ancient system of troughs and valleys in the Amenthes quadrangle

Amenthes quadrangle

The Amenthes quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey Astrogeology Research Program. The Amenthes quadrangle is also referred to as MC-14 . This quadrangle contains the Isidis basin, a location where magnesium carbonate was found by...

 of Mars

Mars

Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

, located at 20.2° north latitude and 233.4° west longitude. It is 317 km long and was named after an ancient river in Greece

Greece

Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....

. Some authors have identified these structures as outflow channels

Outflow channels

Outflow channels is the term used to describe extremely long, wide swathes of scoured ground on Mars, commonly containing the streamlined remnants of pre-existing topography and other linear erosive features indicating sculpting by fluids moving downslope...

, but their origin and history remain ambiguous.

Hebrus Valles has tributaries

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

, terraces, and teardrop shaped islands. These features are all characteristic of erosion by fluid flow, but may or may not support the identification of this feature as carved by a single catastrophic outburst flood of water (as the term outflow channel would imply).