Lethe Vallis is a valley in the Elysium Planitia on Mars, located at 4° North and 206.5° West.

It is 225 km long and is named after river Lethe in Katmai National Monument, Alaska, USA.

[1] Lethe Vallis originates at the SE margin of the West Elysium Basin (Cerberus Palus).

West Elysium Basin probably contained a lake that was 500 km across and received water from Athabasca Vallis.

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