This is Quadra Island.

One of the Gulf Islands in the Strait of Georgia between mainland Canada and Vancouver Island.

It is a beautiful place.

The ice sheet was here not long ago, scraped and polished this bedrock.

And now we have some studying to do.

What does the bedrock tell us?

If you listen carefully, you can hear a collision between microcontinents out in the Pacific Ocean more than 100 million years ago.

I teach Geology 101 at a university, and early in the term, we always go through the laws of relative age dating.

and the law here, that works beautifully, that's on display is the law of cross-cutting relations.

Here's how it works.

We've got this white stripe cleanly cutting across these gray things.

You can see these layers of gray continue on the other side of the white stripe.

But they don't go through the white stripe.

So the white stripe is cutting across the dark layers.

What's the rule say?

If you cut across something else, you got to be younger.

So the dark has to be older than the white.

Makes sense, doesn't it?

Now this works on all scales.

It can be down here under my fingertips, or you can realize that the entire cliff here, right above tide, shows the same relationship.

These swirly dark layers are then abruptly getting chopped off, and this big vertical, light colored thing is the same exact thing as this white stripe down underneath me.

The dark is older than the light.

So what is the dark stuff?

The dark colored stuff out here, it's all limestone.

A little bit of chert beds that are black, but for the most part, it's a limestone story.

And look at the folding.

You can see it, can't you?

It takes your breath away.

I've never seen folds like this in limestone.

So why did these folds happen?

When did they happen?

That's later in the episode.

But for right now, can we be satisfied with the idea that limestone cannot be formed in Canadian climates?

Limestones form under warm, shallow seas.

They form close to the equator.

This is equatorial limestone that was made 225 million years ago.

The Quatsino Limestone.

And it got moved up here to Canada at some point since 225 million years ago.

That's a journey through the Pacific.

That's the story with the limestone.

How about the younger, light colored stuff that's cleanly cutting through the folded limestone?

The white stuff.

It's granite.

Igneous.

Igneous rocks used to be molten material.

Magma.

So these magmas are squirting up through the folded limestone.

You can see it, and it's dying out into these little fingers and forks and they pinch out to nothing, and there's multiple generations.

But this is granite, just like you see in your kitchen countertop.

Coarse grained.

Quartzes and feldspar right here This is not alone.

This is one of thousands of granitic intrusions known collectively as the Coast Plutonic Complex, that dominates western British Columbia.

But the wild thing here is that this 175 million-year-old granite is injecting into this limestone out in the Pacific.

There was a party in the Pacific to fold the limestone and then have this white stuff inject through.

What is the global tectonic story with these rock units on Quadra Island?

Can we tell a big story?

I think we can.

What do we start with?

The limestone.

That's the oldest stuff here, right?

It's folded limestone that formed near the equator.

But the limestone was built on top of a huge oceanic plateau made of Karmutsen Basalt 225 million years ago.

The Karmutsen was built, many geologists think, on top of the Galapagos mantle plume.

So if the limestone says we're close to the equator, the basalt beneath it says we're at the equator, 225 million years ago.

Then we start our journey north.

Some ocean plate starts moving this stuff to the north, and during the journey north, we do the folding.

Why?

There must have been some sort of collision between micro continents.

The oceanic plateau colliding with an island arc.

Who knows?

But we know that collision happened before 175 million years ago.

Because that's the age of the unfolded granite squirts, the white stuff.

So you can see how these cross-cutting relation rules combined with ages for these rock units tells this story.

Is there mystery involved?

Sure.

Mysteries will always be part of geology, but we can reason out a story beginning, middle and end.

And we've got it here.

Quadra Island, southern British Columbia, Canada.