Triceratops lived in the late Cretaceous of North America. Their fossils are abundant in an area now known as the Hell Creek Formation. At the time, this area was a flat, forested floodplain with a relatively subtropical climate. This climate supported a variety of plants, including angiosperm trees, conifers, ferns, and ginkgoes. In this area, streams criss-crossed a coastal plain along the edge of an inland sea.