Geology of the National Parks

GeoMations and GeoClips


This week, we feature one GeoMation and three GeoClips. The GeoMation focuses on "detective work"—the kind employed by geologists to trace and identify the geologic histories of the features and structures they study. The GeoClips take you out to Capitol Reef and Bryce with the CAUSE class, to see a little bit about how the detective work is done in the field. The real detective work involves more rainbows and rattlesnakes than you'll see here; for that, you might have to come see us about majoring in Geosciences.

We hope you enjoy this unit's multimedia presentations and that they help you make a little more sense out of Unit 9.


The Cake
Click Here for Transcript of The Cake Video

It's the weekend, and you're baking a cake for the game for the big game. And so you put down a layer of cake like this. And then it's gotta be for the Penn State game. So then you're going to put in a little blue icing, so it's more enjoyable. And you're going to make another layer cake on top of that, still sitting there. Boy, you're a good baker. It's really very impressive.

And we'll put some more Penn State blue icing in the middle. And then you put down one more layer of cake to make the top of the thing. And wow, this is getting to be fairly serious when all is said and done. And then you're going to ice the top of that, and wow, isn't that beautiful.

And then you want to put some candles on. It's going to be Wisconsin game, and Wisconsin's going to get burned. So you better put on some Wisconsin red candles, and they have a little wick sitting out the top of them like that. And then you're carrying the cake across the floor and your big dog comes up and takes a gimungous bite out of your cake, which doesn't necessarily make you entirely happy. And so now your cake is going to look something more like this with this big hole out of it. And the hole goes all the way down, something like that.

Oh dear, what a mess the dog made out of the cake. And you're really very, very unhappy about what your dog did to it because you were carrying the cake while this happened, and you happen to know that if you're carrying the cake while it happens that you may lose your grip, and the cake turns upside-down, which is now a real mess, and the candles gets scrunched, and so they're no longer sticking down the way they're supposed to be. They're actually sort of sticking off to the side the way they get bent over.

Now, if you were to see this, if you were to find this cake on the floor, you would have absolutely no trouble telling what happened, and the sequence of events in which they happened. In the same way, a geologist faced with something such as a rock viewed edge on that has some mud cracks in it like this, there's a crack, says oh, this rock is right-side up, it has not been turned over because we know that when mud cracks, that the cracks go down in the rock, not up.

In the same sense, if the geologist was faced with some sort of a footprint, and let's make a dinosaur footprint here, if you would like to. Do, de-do, de-do. Here's the big footprint. OK. And the footprint is stuck down in the rock, something like that. And so you can see this is how it might have happened somehow. And that's not the world's finest footprint drawing, but you get the idea what we're trying to do. That has been shoved down into a rock so there's a big hole here where the footprint was made.

If you were to happen to find that footprint, and you're going to have to find that footprint as being upside-down, as we can make it very easily with the foot vertically, you wouldn't know that. And so geologists do that. They can put things in order in the same way you that could look a that squished cake and put it in order.

Dr. Richard Alley


Oysters! - Capitol Reef National Park

Rocks reveal how and where they were formed. What is in a rock, how it is put together, whether the pieces are big or little, sorted or mixed, angular or rounded, and so much more provide clues. Fossils also provide clues. Here, Dr. Alley and the CAUSE class are out in the desert at Capitol Reef National Park, but they are also in a shallow seaway from long ago. See why.

Oysters! Capitol Reef National Park
Click Here for Transcript of Oysters! Video

So we've been driving around the West, pointing at rocks-- there's a rock-- and saying, this is a sand dune. This is a lake. This is an ocean. But we haven't spent a lot of effort on, why do we say one is a sand dune, and one is a lake, and one is an ocean? Now in the case of the sand dune, when we looked at it, it was all sand. There were no little pieces, there were no big pieces, it was all intermediate size sand pieces. They had these structures that one sees in modern sand dunes. If you found anything that looked like a fossil, it was little reptile tracks. And so they had all the characteristics that you see in a modern sand dune.

Now here, we're in rocks that are very different. The rocks behind us are sort of washing away and they're making mud that washes down around our feet. And there's a number of characteristics of these, the layers are different, how big the grains are in them is different, sort of everything about them is different. And we can say these were rocks that were underwater. And we can go through the whole list of reasons why we can say they're underwater, but there's one very easy one. If we look down at our feet, and we look around at what's washing out of these rocks, what we find is oysters. And one can be very confident that if you find rocks full of oysters, you're not in the middle of the desert.

Dr. Richard Alley

Mud Cracks - Capitol Reef National Park

Rocks occasionally are turned upside-down, but nature tells us when that happens. Mud cracks can show us that; they are wide at the top, narrow, and then end at the bottom. Fill mud cracks with another layer of sand or mud, and the cracks are "fossilized," to tell us which way was up when the rocks were deposited. Here, visit Capitol Reef with Dr. Anandakrishnan to see mud cracks, with a brief look at some right-side-up ones from the Grand Canyon.

Mud Cracks
Click Here for Transcript of Mud Cracks Video


Look at this picture. You've got all these cracks developed over here. Imagine a second flood coming through here, a relatively gentle flood, water slowly flowing in here, a new layer of silt and sand and shales and clays. What's going to happen? All of that new material is going to filter down into these cracks and it's going to solidify in there as the water evaporates out of it.

So now 100 million years goes by. And we come along and we cut this open and we look at this layer and we look at these, and you'll see mud cracks. And we'll be able to tell that that layer of rock was oriented this way, because these mud cracks all start wide at the top and get narrow going downwards. And it quite often happens that these strata of rock, because of the incredible forces of nature of plates coming together, will take these layers and just flap them over upside-down. And we come along and we look at them, and you can't tell which way is up, which way is down until you find one of these mud cracks.

And then, even if the layer's upside-down, then you'll have these mud cracks teepeeing upwards. And you'll say, whoa-ho, this thing must've been flopped over and turned over upside-down. And it's the same processes-- I'm doing a Richard here. It's the same processes that produce these mud cracks, will fill them in, and then maybe after 100 million years, they'll get fossilized, turned into a hard clay layer, and then turned upside-down. But we'll still be able to tell what we call the stratigraphic relationship, the time relationship, which is older, which is younger, because clearly this is older than whatever would lay on top of it.


Dr. Richard Alley

Conglomerate within a Conglomerate- Sevier Fault near Bryce Canyon National Park

Geologists read rocks, and the stories are fascinating--historical novels full of intrigue. In this next GeoClip, Dave Janesko and Dr. Alley perch high up in Red Canyon just west of Bryce, and read one of those stories of deep time.

A conglomerate is a sedimentary rock in which many of the clasts are bigger than sand. Dave and Dr. Alley are looking at a conglomerate that includes many different clast types, including one that is itself a finer-grained conglomerate. The clasts in that conglomerate-within-a-conglomerate include several types of sedimentary rocks, including sandstones that are themselves made from older pieces.

Click Here for Transcript of Conglomerates Video

Um, maybe. I can kind of break it out.

No, that's a conglomerate, isn't it?

Yeah. It is. Look at that, Dave. That's the conglomerate we were looking for. Just look at that! Isn't that a beauty?

It is.

A conglomerate in a conglomerate. What do you make of the class in the little one?

It looks like sandstone and limestone to me.

Deep time. Deep time!

Very deep.

We got deep time! This is just beautiful.

A conglomerate classed in a conglomerate?

A conglomerate, you have to have sand grains glued together to make sandstone, broken and rolled to round them off, because this is rounded. And you have to have an ocean or a lake that has things living in it, precipitating calcium carbonate to make a limestone, broken loose and rounded off. And then those have to get together in a beach or in a stream channel. They have to be deposited with sand around them, then they have to be cemented together with hard water deposits. Then that has to be broken out, rolled in a stream and rounded, put together with all these other rocks coming from every which way. All of those then have to be glued together with hard water deposits. And then we have to get from the stream or the lake or whatever it was that was making these, up here in the middle of the desert on a cliff. And it's all in that one rock right there. And there's really no other way to explain that rock.

In geology, we often meet people who tell us that we do not know what we're talking about, that the world looks like it is very, very young, that there's nothing in the world older than written history. We never tell those people that they're wrong, that they're false, that they've been led astray. But we can tell these people, it looks old, that the scientific interpretation, the best way to look at these rocks, is that they tell of vast, deep time. So when one looks at a rock like this one that has little tiny remnants of old rocks glued together into a rock which is bounced around in the stream and rounded, that then is glued in with a whole bunch of other rocks into another rock that has been bounced around in a stream and rounded, that is sitting here glued with a bunch of these things on a cliff in the desert-- it is very hard to imagine how this could be something that is only 6,000 years old. And so all we do in science is, what can we observe? What can we test? And what we can observe, what we can test says, really, really old.

Dr. Richard Alley

Want to see more?

Optional Enrichment Article (no, this won't be on the quiz!): What do beauty, saving money at Las Vegas, religion, oil exploration, emerging new diseases, and the planet’s recovery from global warming have in common? All in some way involve deep time, the immense age of the Earth. Eric Spielvogel filmed a discussion of these and other issues with Dr. Alley, for a special “time” issue of Research! Penn State. The Deep Time film clips on the next page will give you something to think about, and may even help with the course. Enjoy! Also, here are some optional animations you might also want to explore! (No, these won't be on the quiz either!)

Sedimentation Models
(An extensive collection of animations on this subject)

Sequence Stratigraphy
(An extensive collection of animations on this subject)