Welcome to the William O. Douglas Wilderness Area in the Central Cascades, in the state of Washington.

And that's Mount Rainier, an active stratovolcano today.

We have five of them in our state.

But what if I told you, if we go back into the history of the Cascades, there were dozens more that used to stand at different places, but had similar shapes to Mount Rainier or Mount Adams.

Where did one of those ghost volcanoes used to stand?

Right here at Cash Prairie.

There's been a lot of careful work up here in the mountains of the Cascades by geologists.

We now realize there's a 46 million year history of volcanic activity in the Cascades.

But does that mean that Mount Adams here, over my shoulder, is 46 million years old?

The answer is no.

Individual stratovolcanoes in the Cascades have a 2 million year life span, and Mount Adams is only 1 million years old.

And Mount Rainier is younger than that.

It's half a million years old.

So this life span is a real thing.

There's a million and a half more years of life for Mount Rainier before it totally goes away.

The magma will stop rising.

The mountain will be cold and will be crumbling through erosion.

That concept of totally erased volcanoes, that's the ghost volcano idea.

And there are bones of all of these old ghost volcanoes all through the low country of the Cascades.

You just have to know where to look.

This is a hiking trail full of pumice.

You can see it.

I've got a block right here to show you.

This is up on Cash Prairie.

More than 6000ft elevation.

It's a nice little secret spot high in the Cascades here.

This pumice is fragile.

It's got holes in it.

Gas bubbles.

It's got broken blocks of other volcanic material, and the key point is, if you find pumice lying loose on the ground, that means you are nearby to an active volcano.

And maybe the eruption was just a few hundred years ago, or maybe a couple thousand years ago, and the pumice fell through the sky, came from that erupting volcano, like Mount Rainier or Mount Adams.

I can see them right now, but the dirty little secret is this is not pumice.

I know it looks like it, but it is not.

It's too heavy.

The heft of this stuff is wrong for pumice.

And in fact, this material is the top of a thick layer of bedrock that makes up Cash Prairie, that's 25 million years old, and tells a tale of a volcanic explosion, much older and much bigger than what we were just trying to visualize a couple of minutes ago.

Let's drop over the ridge and look at that bedrock.

So our quote unquote pumice is not pumice.

It's right there on the trail.

But what did we just decide?

We decided that those loose blocks did not form in loose blocks.

They formed in this solid mass of bedrock.

And this thing rings.

This thing is solid.

And it's been dated at 25 million years old.

This is the tuff of Cash Prairie.

It's an ash flow tuff, meaning there was a volcanic explosion here 25 million years ago.

You take a cone volcano and you blow it up, and you have a traveling, ground hugging cloud of white hot ash and gas and rocks.

You can see some of the rocks that were swept up in this ground hugging hurricane of hot rock.

And eventually that pyroclastic flow runs out of energy.

It sits, it loses its heat, and it welds together into this permanent record of what happened that long ago.

So we're thinking about what ghost volcanoes are in this episode, right?

A cone volcano that once stood, and after 2 million years, it gets eroded away completely.

Just erased from the record.

This tuff of Cash Prairie, which is 25 million years old.

It's the thickness.

It's the scale.

You can see how much of this white bedrock layer is here.

That's the evidence of a cone volcano that used to stand right here at Cash Prairie.

Can we please bring in a cone?

Can we please plop it right down here in this particular piece of real estate in the Cascades?

Can we have it exist for 2 million years?

And then can we please erase right now?

Can we erase that cone?

And what's left?

The volcanic products that erupted out of that cone.

It's the layers that outlived the source.

And so when we look at volcanoes today, like Mount Adams, you and I hopefully now realize that Adams is not a permanent cone on the landscape.

It will also disappear at some point down the road.

Adams is about a million years old, so we have another 1 million years of time before Adams gets erased, and underlying bedrock marks its spot in the long, dramatic history of Cascade volcanic eruptions here in the state of Washington.