Dates	Period	Physical/Biological Features
136,000,000 – 65,000,000	CRETACEOUS	Rocky Mountains began to rise; most plants, invertebrate animals, fishes, and birds of modern types; dinosaurs reached maximum development and then became extinct; mammals small and very primitive.
190,000,000 – 136,000,000	JURASSIC	Granite foundation of Sierra Nevada laid down; conifers and cycads become dominant among plants; primitive birds appeared.
225,000,000 – 190,000,000	TRIASSIC	Lava flows in East North America; ferns and cycads dominant among plants; modern corals appeared and some insects of modern types; great expansion of reptiles including earliest dinosaurs.