Twin Mountains Formation

Twin Mountains Formation Stratigraphic range: Early Cretaceous
Type	Geological formation
Unit of	Trinity Group
Underlies	Glen Rose Formation
Thickness	150 ft (46 m)
Location
Region	North America

The Twin Mountains Formation, also known as the Twin Mountain Formation, is a sedimentary rock formation, within the Trinity Group, found in Texas of the United States of America. It is a terrestrial formation of Aptian age (Lower Cretaceous), and is notable for its dinosaur fossils. Dinosaurs from this formation include the large theropod Acrocanthosaurus, the sauropod Sauroposeidon, and the ornithopod Tenontosaurus. It is the lowermost unit of the lower Cretaceous, lying unconformably on Carboniferous strata. It is overlain by the Glen Rose Formation. It is the lateral equivalent of the lower part of the Antlers Formation.