The Hornitos Formation is a Campanian geologic formation of the Algarrobal Basin in the Atacama Region of northern Chile. The formation comprises limestones, sandstones, conglomerates, marls and tuff. Dinosaur remains are among the fossils that have been recovered from the formation, including the sauropod Arackar licanantay.

The Hornillos Formation, deposited in the Algarrobal Basin, comprises sandstones, limestones, conglomerates, and caliches, intercalated with lavas and andesitic breccias and various volcanic rocks. Between these last is a conspicuous layer of rhyo-dactitic lithic tuff, which reaches up to 10 metres (33 ft) in thickness. Bones of indeterminate titanosaurs appear in a marly limestone stratum of 10 metres (33 ft) thick with decimeter-sized calcareous concretions. The smallest pieces were found as rollings, whereas the larger piece was included in the limestone.

The Hornitos Formation formerly was thought to be of Paleocene to Eocene age. The formation may be older and belong to the Early Cretaceous, as a granite intruded the rocks about 105 ± 10 Ma.

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Sauropods of the Hornitos Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Arackar	A. licanantay	Atacama Region	Campanian to Maatrishtian	Femur, Humerus and Ischium	A lithostrotian titanosaur; closely related to Isisaurus colberti.

• List of dinosaur-bearing rock formations
  • List of stratigraphic units with indeterminate dinosaur fossils
• Abanico Formation

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• G. Chong Diaz. 1985. Hallazgo de restos oseos de dinosaurios en la Formación Hornitos – Tercera Region de Atacama – Chile. IV Congreso Geologico Chileno 152–161
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