I love Leavenworth, Washington, and maybe you do too, especially in the springtime.

Come on, it's hard to beat this area.

The geology is spectacular as well.

Towering granite mountains of the Stuart Range, and in the Wenatchee River valley: Sandstone.

Sandstone going five miles deep in this sedimentary basin.

That's not new information, but what is exciting and brand new are discoveries within the sandstone layers, special layers that give us brand new information about a dramatic era of volcanic eruptions and tectonic uplift more than than 40 million years ago.

So this place is surrounded by mountains of granite.

But this is sandstone.

Those rocks are actually made out of the same minerals, so it is difficult to tell the difference between granite and sandstone.

How are you supposed to do it?

Here's one way.

Take a rock hammer.

Wail on the outcrop.

That soft thud sound is a sandstone sound that's a sedimentary sound as opposed to a granite from nearby Mount Stuart.

That has a ting to it.

This is a harder rock.

It's an igneous rock.

So can I show you the details of the minerals?

Even though the minerals are the same in the granite and the sandstone.

Here's what the minerals look like inside of a granite.

They're sparkly, interlocking jigsaw puzzle pieces that were all cooling together from an originally hot magma chamber, underground.

The sandstone is different.

Same minerals - quartz, feldspar and mica.

But there's far less sparkly.

There's individual sand grains that are loosely held together.

That's why the soft thud sound and these are cool rivers flowing gradually, as opposed to a hot magma underground.

But is all of the sandstone the same grain size?

Hello from the Chumstick Basin.

Look at this outcrop with all these layers Frame left, far away from me is gorgeous, typical looking sandstone of the Chumstick.

Medium grain sand deposited by a steady river flowing into this basin.

If you start coming my way and start digging into some of these layers, we lose the regular river scene.

We get into some fine grain muds, full of plant fossils, organic rich, and so our energy has dropped.

And then if you keep coming my way, it looks like you're doing a nice job.

We increase to river cobbles and the cobbles get bigger and bigger until we have beautiful bowling balls, completely rounded.

So the energy necessary to move this is far greater than the energy to move just a couple of grains of sand in a normal Chumstick sandstone.

Why is the energy so great?

Why is the water moving so fast?

To move, polish and drop these bowling balls in this conglomerate within the Chumstick Basin?

The answer is that the ridges are rising, the floor is dropping in dramatic fashion, and so whitewater rivers are hauling out of these uplifting mountains, coming into this sandbox with the floor dropping, and the net result is five miles of total vertical thickness of the Chumstick sandbox.

Looks like more sandstone, doesn't it?

But do you hear that?

These resistant ledges are hard.

They're tough.

In fact, they are actually volcanic tuff beds.

20 feet of volcanic tuff that's inside of this sandstone sequence.

Let me show you what a volcanic tuff looks like.

These sparkly crystals are all forming simultaneously during a super volcanic eruption.

To the north of here, we had ash erupting and falling, burying a river scene here in the Chumstick sandbox.

So you can't date sand very well.

The sand grains are of different ages from different places, but you can get a precise date on an igneous layer within a sedimentary basin.

And that's what this tuff, and more than a half a dozen tuffs have been found to do, here in this sedimentary sequence.

The tuffs go from 49 million years ago to 46 million years ago.

We can keep track of time within the sandbox by getting a precise date for each of these tuffs.

So the idea is, if we know the ages of the tuffs, we can keep track of how much time is elapsing as we're dumping the sediment into the basin.

So the sedimentation rates are absolutely world class and a huge surprise.

So much sand and river cobble material coming into this basin at a record pace.

Let's zoom out in the last segment of this episode and talk about why this basin is forming when it decides to form.

Sandstone?

Yes.

Granite?

No.

49 to 46 million years ago.

How do we know that?

The volcanic tuff layers that are inter bedded within the Chumstick sedimentary sequence.

That's exciting, but it's not happening anymore.

This is a fossilized sandbox.

Why 49 million years ago?

Well, shortly before that, Washington collided with a huge island out in the Pacific known as Siletzia.

And the result of that collision is the reason that this floor started dropping and these ridges started rising so dramatically back at that time, during the Eocene.

And 46 million years ago, everything stopped.

This basin stopped doing its dumping story because the Cascade Volcanic Arc was just getting started with a subducting ocean plate.

And you can't do that at the same time that you're doing today's story of pulling apart, dropping, lifting.

All right here, geologically, at Leavenworth, Washington.