The Arén Formation or Arén Sandstone (Catalan: Calcàries i gresos d’Areny)[1] is a geological formation in the Tremp-Graus Basin around Arén, Catalonia, Spain whose strata date back to the Late Cretaceous.

[2] Dinosaur remains are among the fossils that have been recovered from the formation.

[3] The formation dates to the Campanian to Maastrichtian and underlies the Tremp Group.

Dinosaur eggs (Megaloolithus baghensis,[4] Sankofa pyrenaica),[5] sauropod tracks, unnamed sauropod remains, theropod tracks, euornithopod tracks, and an unnamed iguanodont remains present in Lérida Province.

It is a place in Vilamitjana municipality known by the finding of an important paleontological site.