The Hell Creek Formation is a large area of rock outcrop in America. Mainly in the state of Montana, it is well studied formation where many of the most famous dinosaurs come from like Tyrannosaurus rexand Triceratops.
The formation is made up of layers of rock. These rocks are formed from sand and mud from rivers that flowed over 65 million years ago. As more and more sand and mud were deposited by the rivers, slowly the layers built up. This process is sedimentation.
The formation is up to 172m thick and was formed in about 1.2 million years. The end on the formation also marks the great extinction that ended all dinosaurs except birds.
Here are some of the Dinosaurs from the Hell Creek Formation, Click on their names to find out more.