 What do I see when I look at this figure? Well, there's four plates shown here, the North American plate, the Rivera plate, the Pacific plate, and the Cocos plate. Let's make sure we understand how they're all moving relative to each other. Well, over here, there's a ridge between the Pacific plate and the Rivera plate, and that's a divergent boundary. So we can draw some arrows to show which way they're moving. So this is a spreading center. And now these arrows I've drawn, luckily, they jive with the transform fault down here between the Rivera plate and the Pacific plate. So the Rivera plate's moving from west to east, and the Pacific plate is swinging up to the east. Now this is kind of a complicated area because this is where three plates come together, and clearly the authors who drew this figure weren't exactly sure how that worked. But since there's some normal faults here, my sense is that the Rivera plate and the Cocos plate must have some motion between them that might be pulling apart. But where exactly this boundary between all three plates is kind of complicated, obviously. Well, so there's still a Cocos plate and the North American plate. And there's a great big subduction zone that runs along like this. And I'll draw the teeth on it a little bigger so you can see it better. So the teeth are usually drawn on the overriding plate, and that means that we've got a subduction zone where the Cocos plate is heading this way, and the North American plate is heading that way. The Cocos plate and the Rivera plate at an oblique angle are diving underneath the North American plate at this boundary. Now this boundary right here that I'm sort of marking out in red, this is just the boundary between the ocean and the land. So this is the shoreline. The North American plate is everything on land plus this amount of continental shelf before you get to the trench. And then the Cocos plate, Rivera plate, and Pacific plate are all out in the ocean. So this big subduction zone is probably the most important thing for our discussion. And as these plates go down this trench, they're causing volcanism and uplift back here on the continent. And that's where the Primavera caldera is located back in here.