Eocene Epoch 55-34 million years ago Plate tectonics and volcanic activity form the Rockies in the western North 
(Eocene Epoch; Plate; tectonics and volcanic activity form the Rockies in the western North; T:55-34 million years ago)
Eocene Epoch
Plate
tectonics and volcanic activity form the Rockies in the western North T:55-34 million years ago