Question: Which geologic formation is found in the northern edge of Patagonia?

Related documents: [0]  [DOC] Río Negro (] , "Black River") is a province of Argentina, located at the northern edge of Patagonia. Neighboring provinces are from the south clockwise Chubut, Neuquén, Mendoza, La Pampa and Buenos Aires. To the east lies the Atlantic Ocean. [END] 
[1]  [DOC] The Portezuelo Formation is a geologic formation outcropping in the Mendoza, Río Negro and Neuquén provinces of Argentina. It is the fourth-oldest formation in the Neuquén Group and the older of the two formations in the Río Neuquén Subgroup. Formerly, that subgroup was treated as a formation, and the Portezuelo Formation was known as the Portezuelo Member. [END]  
Answer: Portezuelo Formation
Portezuelo Formation