Out of the GR 65 but this trail is excellent for mountain bikers. It is signedposted "Tour des Monts d'Aubrac". Fantastic lunar landscape.
From Aumont Aubrac follow "Tour des Monts d'Aubrac" signs. The ride is quite easy through Prinsuéjols, le château de la Baume, St Laurent de Muret, then becomes wilder aroud Bonnecombe.
5 km after the shelter, go to the west (Aubrac ou St Chély d'Aubrac) next to the dried up lake. Then we chose to go north est on the GR65A, hardly signedposted and a bit swampy. Take the little road to Montorzier and the sigletrack that leads to the D52 road.
You can have a look at the St Andréol lake, but after the lake, there is not many signposts so it is best to go back to the D52 to Montgros.
There you will find the GR 65 which will take you easylly back to Aumont Aubrac (you will have to open and close a dozen of little doors).