The Huitrera Formation is a geological formation in the Neuquén Basin in northern Patagonian Argentina whose strata date back to the Early Eocene of the Paleogene, or Casamayoran in the South American land mammal age classification.

The name has been used to identify various volcaniclastic sequences, among others in the Ñirihuau fold-and-thrust belt.

[2] The up to 1,300 metres (4,300 ft) thick formation comprises mudstones and sandstones deposited in a crater lake environment.

Part of the formation comprises andesites, dacitic and rhyolitic ignimbrites, volcanic breccias, tuffs and trachybasalts.

[3] The formation was initially described as Late Eocene to Early Oligocene, but was later dated to 54.24 ± 0.45 Ma, meaning the Huitrera Formation is Ypresian, or in the SALMA classification, Casamayoran in age.