- [Teacher] What does it mean to be curious?

For my students, curiosity creates opportunities for a bigger and brighter future.

(pensive music) - There's a basic rule in Geology 101.

If you have sedimentary rock layers, they are created horizontally, always around the world, like in the Grand Canyon and like here at Big Four Mountain.

But if you start following those horizontal layers here to another cliff, those horizontal layers are now vertical.

And something happened starting 51 million years ago to rotate these sedimentary layers to such an extreme position.

What happened here?

(pensive music) (soft music plays) The sedimentary layers here involve a river and involve sand.

I mean, this is river sand.

We all know what sand is, but this is not beach sand.

This is river sand.

And these sand grains are all about the same size, but they're not the same mineral type.

They're salt and pepper sand.

And so therefore, the sand stones deposited horizontally before the Cascade mountains even developed between 59 and 51 million years ago, with rivers flowing from the northeast and flowing to the ocean are these beautiful arkosic sandstones.

This is normal sand deposition.

A deep sandbox stretching from Bellingham over to Ellensburg before the Cascade mountains grew.

No big chunks, normal, horizontal, fine sand.

(bouncy music) Okay, river deposition, river sand, making sand stone we're good.

But there's also sedimentary rock here that looks like this.

And it's rock.

It's a conglomerate.

And each of these beautiful stones is rounded and they're made out of a rock called chert.

White and black chert river cobbles.

That means that a river was suddenly more energetic, faster water, higher energy, and better than that, the rivers that deposited these grains were flowing towards the east coming away from the coast.

Something caused these rivers to change their direction flowing west before 51 million years ago, the rivers are suddenly flowing to the east, younger than 51 million years ago.

And the evidence is, there's exposed chert beds, black and white, just to the west of here.

So these stones in this conglomerate tell us that the rivers flipped their direction 51 million years ago, increased their energy level, and by the way, at the same time, the chert beds are rotating to the 90 degree position.

What's causing all this strangeness in these local sedimentary basins?

(soft guitar music) So here's the answer.

Before 51 million years ago, out in the water, off the coast of Washington was a huge island called Siletzia.

Bigger than Iceland, but similar with Basalt lava erupting.

North America collided with Siletzia starting 51 million years ago, causing the rivers to change their direction, causing chert cobbles to flow away from the impact site, and the result is inclined sedimentary beds at Big Four Mountain in Northwestern Washington.

(soft music plays) - [Announcer] This series was made possible in part with the generous support of Pacific Science Center.