The Cerro Fortaleza Formation, in older literature described as Pari Aike Formation, is a Late Cretaceous geologic formation of Campanian to Maastrichtian age[1][2] (although it has formerly been reported to be Cenomanian to Santonian)[3] of the Austral Basin in southern Patagonia, Argentina.

The sandstones of the formation were deposited in a fluvial environment.

The formation has an estimated thickness of 460 metres (1,510 ft) and overlies the Anita Formation, while it is overlain by the La Irene Formation.

[4] These formations are considered Campanian and Maastrichtian in age, respectively,[4][3] making the Cerro Fortaleza Formation aged between them.

The giant titanosaurs Puertasaurus and Dreadnoughtus, the megaraptoran Orkoraptor, the berthasaurid Austrocheirus isasii, and the ornithopod Talenkauen have been recovered from the formation alongside turtles and crocodiles.