Okay, so imagine you're making a sandcastle at the beach. You start by piling up a big mound of sand, right?
Well, millions of years ago, there was a huge mountain made of rock instead of sand. This mountain was called La Garita, and it was located in what is now southern Colorado.
But here's where it gets really interesting. Underground, there was a bunch of super hot melted rock called magma. The magma was so hot that it eventually pushed its way up through the mountain and created a massive hole called a caldera.
Now, this caldera was huge - around 20 miles wide! That's like the size of 20 big cities put together. And it wasn't just a regular hole - it was filled with all sorts of crazy things like ash, lava, and hot gas.
So basically, La Garita Caldera was a super big hole in the ground that formed because of hot melted rock pushing its way up through a big old mountain. Cool, huh?