If we could go back, let's say 10 million years ago, the rocks that are forming that cliff behind me would we would be underneath those rocks today because that is an erosional cliff.

And so over the last 10 million years or so, the cliff has been moving off to the north because of erosion.

A lot of geology is really a history.

It's Earth history, trying to understand what events happened and how they occurred.

It's really a fantastic science because it's not really a science in unto itself.

It's an amalgamation of all sciences applied to a very complex system, which is the earth.

Geologists tend to be fairly patient.

Because you know, a million years is a blink of an eye for a geologist.

What's in the Book Cliffs behind me is quite interesting from, again a geologic history perspective, are a series of sandstones that are very, very tabular, meaning flat, like pages in a book.

And then there are shales, and the sandstones that form the cliffs some of them are actually ancient beach deposits.

Back in probably the late 1800s or early 1900s, the geologic surveys that were coming through here made the notation that those sandstones and shales looked like the upturned pages of a book.

And of course, the pages are very thick respectively.

But that's where the name comes from.

If we could be here in the same location, roughly about 70 million years ago, we would be actually underwater.

Back in what's called the Cretaceous period this whole part of Colorado, in fact, the whole Rocky Mountain region was the site of a shallow seaway.

And all of this Mancos shale that you're looking at here was deposited sea bottom mud.

And so this Mancos shale, which is by far the thickest sedimentary rock here in this part of Colorado, it's about 5000 feet thick, represents millions of years of sea bottom mud.

How would you know it's sea bottom mud?

The shale has a lot of fossils in it, and the fossils are squid like animals or clams or shark's teeth.

So the shale includes a lot of fossils indicative of how the original mud was deposited.

The rocks on the top of the Book Cliffs up there are sandstones that [are] what we call shoreline or ocean margin type deposits.

And so you have deltas and you have beaches and you have incised canyons that got backfilled with sand.

That's what makes the top of the Book Cliffs.

But it didn't just happen once.

The reason you have layers is because this is happening cyclically.

Everything gets eroded eventually.

And we just happen to be seeing the erosional edge of them.

You can break a rock apart using a physical force, or you can just let rainwater mixed with oxygen and carbon dioxide chemically break down the rock.

And so it's a combination of chemical and physical weathering.

You know, everything we're walking on is in the process of being destroyed slowly.

So there is your very own piece of sea bottom mud let's just leave it at that.