Labou Vallis is a valley in the Memnonia quadrangle of Mars, located at 8.7° south latitude and 154.5° west longitude. It is 222 km long and was named after a French word for Mars. Labou Vallis has dark slope streaks on its walls. The streaks are generally thought to be the dark material that has been exposed by bright dust moving down a steep slope in an avalanche.