The mountain Aup has at its origin the name Alpage (high mountain pasture) in patois (old local language), mountain pastures that mainly compose the mountain. It is located just beside the Rognon. From Spring until the end of the summer, this mountain is used as place of "transhumance" for many herds of cows and sheep.

An earth path permits to leave from the village Lalley to reach the bottom of the mountain Aup, at about 1400m high, where a sheep-fold is.

At an altitude of 1796 meters, the Aup is a precipice on the side of Tréminis. It is a very nice jaunt and much easier than Rognon.