The Anacleto Formation is a geologic formation with outcroppings in the Argentine Patagonian provinces of Mendoza, Río Negro, and Neuquén. It is the youngest formation within the Neuquén Group and belongs to the Río Colorado Subgroup. Formerly that subgroup was treated as a formation, and the Anacleto Formation was known as the Anacleto Member. The Anacleto Formation varies between 60 and 90 meters thick, and consists mainly of claystones and mudstones, purpleand dark red in color, of fluvial origin. Geodes are often found scattered throughout this formation.