If you've ever wondered how the American West got so many lovely and awe-inspiring rock formations, here's an explainer. The western US was a very active place between 25 and 40 million years ago. The Rocky Mountains were formed by plate tectonic activity, and there were a lot of volcanic explosions, the largest of all happening in Colorado. They call this the "Mid-Tertiary ignimbrite flare-up." The Wikipedia entry for this event is so short and full of jargon as to be incomprehensible. A few graphics and a lot of everyday language would make this a lot more clear, and that's what PBS Eons gives us in this video. They describe the biggest volcanic explosions ever from the earth's past and what caused them. But the big surprise is how plants and animals survived this period without a huge extinction event, which they also explain. This story is a couple of minutes shorter than the video length indicates.