(gentle music) - I'm the superintendent of beautiful Sinks Canyon State Park here in Lander, Wyoming.

I want to welcome everybody to one of the hidden jewels of Sinks Canyon, Boulder Choke Cave.

(stirring music) (stirring music fades) (gentle music) The phenomenon of the Sinks and the Rise is really awesome.

The Popo Agie River totally disappears in a limestone cavern, and then it journeys underground for an eighth of a mile to the Rise.

We take tours in the cave, and me and my staff are really excited to show you guys around.

You know, Boulder Choke Cave, when you walk up to the cave itself, it just looks like a set of boulders.

- [Skyler] Careful of the ice coming down here.

Watch your step.

- And we have a gate there, 'cause we have to keep this cave locked.

For one thing, this cave actually floods out every summer.

Basically you have a gate that you climb down into.

(upbeat music) (upbeat music continues) And then there's about a 25 foot crawl.

And then basically you can stand up, and you're actually in the Boulder Choke.

- [Skyler] So now we're in the main passage of Boulder Choke Cave, and we'll actually be following these passages all the way down to the river.

And the first thing you see when you come in here are the limestone walls.

If you look close to the texture of the walls, you can see all the scalloping within the limestone.

And as the water travels through, it'll just erode and erode away, forming this very unique texture.

(upbeat music) (upbeat music intensifies) (upbeat music continues) We just came down our only manmade structure in the cavern, the rope, down to what we call the Grand Canyon of the cavern.

And if you look up, this is actually the tallest room that we have here, reaches about 20 feet.

And you can start to see how the rock is layering.

(upbeat music) And so the last of the glaciers were seeded out of this canyon, 15 to 17,000 years ago.

It was actually called the Pleistocene glaciation period.

And when it receded, it uncovered the Sinks and the Rise, and that allowed a bunch of water to flow through, and leave behind this entire cavern for us to explore.

(upbeat music) And you'll notice that we're standing on silt, and as the water floods this entire cavern, every single year, it picks up all the sediment and redeposits it throughout the entire cavern.

And so what you'll find are new passages opening up and old ones closing every year.

And so every time we come through, it's a whole new experience.

- For a long time, they didn't know if it was the same water that came in from the Sinks that came up to the Rise.

And in 1983, they did an official dye test.

- [Researcher] We're attempting to find out if the water that goes into the Sinks is the same flow that comes out below.

- [Reporter] Is this dye safe?

- [Researcher] Yes, it's been tested all over the United States.

It's never had any problems at all.

What you can get with the dye is an exact simulation of what's happening in a water body.

Now, the test results consist mainly of the travel time of the dye from the place where we put it in, at the Sinks, to the Rise, where we were able to detect it.

The travel time was about two hours for the dye to first start showing up in the Rise.

And our sampling shows that it took about three to four hours to completely pass, so that there was no more dye left in the pool.

(water rushes) - [Jamie] What we're seeing now is the Popo Agie River running right through the middle of Boulder Choke Cave.

(upbeat music) - And so if you look behind me here at the Popo Agie River, you really see the bulk of the river coming through.

And right now it's running at about 30 cubic feet per second, but during the summer months it can get up to 1,000.

And so this entire area is gonna be completely flooded with water here in a few months.

This is honestly the furthest down the river that we've been able to explore.

Down this cavern behind me, we've been able to send divers, however once they get around this corner, it cuts off.

And so we haven't been able to explore between here and the Rise, which is what really makes this cave one of the greatest mysteries of the canyon is why it takes so long to get from here down to the Rise.

And we have theories of cracks and fissures.

But in all honesty, it's just really hard to determine what's happening down there.

- And like I said, we don't have it all figured out yet, but there're really interesting phenomenons that are going on here in the cave.

It's a living, breathing thing.

(upbeat music) It's great to take school tours in here.

You know, you get a class of third graders or seventh graders that have never been in this cave environment, and turn off the lights into total darkness, physically challenge them.

When they come out of Boulder Choke Cave, a lot of times it changes their whole perspective on not only Sinks Canyon, but of their abilities, and what they've just seen.

(upbeat music) I'm actually from Lander.

I was maybe four or five years old the first time I saw the Rise, and fed the fish.

So it's an amazing place, it's 600 acres, but it's a jewel of Wyoming.

It's such a diverse area with different habitats.

You know, it's my pleasure and my joy to be able to work here, to protect, to inspire, to educate people about this wonderful area, and about all the things that we love and that we do here in Sinks Canyon.