National Park Service Mission
EDUCATION LESSON PLAN
Title: Black Canyon-ology (A lesson about the geology and history of the Black Canyon)
Standards: Geography (3.1) Students know the physical processes that shape Earth’s surface patterns (explaining the variation in the effects of physical processes across Earth's surface) (4.4) Students know the processes, patterns, and functions of human settlement. (5.1) Students know how human actions modify the physical environment (5.2) Students know how physical systems affect human systems (comparing and contrasting how changes in the physical environment can increase or diminish its capacity to support human activity) (6.1) Students know how to apply geography to understand the past (analyzing the fundamental role that places and environments have played in history) (6.2) Students know how to apply geography to understand the present and plan for the future.
History (1) Students understand the chronological organization of history and know how to organize events and people into major eras to identify and explain historical relationships. (1.2) Students use chronology to organize historical events and people (using timelines to organize large quantities of historical information, compare different time periods and places, and answer historical questions) (4) Students understand how science, technology, and economic activity have developed, changed, and affected societies throughout history.
Science (2.1) Students know that matter has characteristic properties, which are related to its composition and structure (separating substances based on their chemical and physical properties)
Teacher: At least two NPS Education Specialists
Materials: Geologic time line cards and rope (1 set per 10 students); hardness scale materials (rock samples, steel file, glass, pennies); maybe a hardness scale worksheet; rock examples (gneiss, schist, pegmatite, quartz, mica (both muscovite and biotite), feldspar, sandstone, quartz monzonite …)
I. INSTRUCTIONAL OUTCOMES
On South Rim Visitor Center (VC) deck: (also explain the rules of LNT, and no rock throwing)
Welcome to the Black Canyon of the Gunnison National Park. People come from all over the United States, and many foreign countries as well, to see this canyon, because no other canyon in North America combines the narrow opening, sheer, steep walls, and surprising depths offered by the Black Canyon of the Gunnison. This area became a national park just a few years ago, in 1999, when President Bill Clinton signed the legislation, upgrading it from its previous status as a National Monument. There are currently 388 National Park Service units throughout the United States. That number includes national parks, like this one, national recreation areas like nearby Curecanti, national historic sites, national scenic rivers, and others. Basically, all of the units managed by the National Park Service are nationally significant, meaning they contain something special, worthy of protection, that can’t be readily found in other areas. Some battlefields are managed by the national park service for their cultural importance, and the role they played in American history. Other areas, like Yellowstone National Park or Denali NP in Alaska, are protected because of the diversity and abundance of wildlife that lives there. Can anyone guess why Black Canyon of the Gunnison is a protected area? Because of its dramatic geologic features.
Today, we’re going to focus on the geology of the Black Canyon, but we’ll also talk about some of the early explorers who visited this area, the railroad that passed through the canyon, and the tunnel that stretches through the walls of the Black Canyon.
III. TEACHING PROCEDURE/METHODOLOGY
At Gunnison Point Overlook:
Let’s start off by traveling way, way back through time. Close your eyes and imagine a stark landscape. All around you, you can see rocks of different colors and different shapes. Some of the rocks are jagged, others are smooth. Everywhere you look there are rocks. It’s a strange scene, because there’s a huge thing missing. Life. No matter where you look, you can’t find anything that’s alive. No plants, no animals, no insects, and certainly no people. Open your eyes. You’ve just visited planet Earth during the Precambrian time, more than a billion years ago. Precambrian means “before life.” There was no life on Earth because it was a time of harsh and drastic changes in the Earth, and nothing could survive.
As you look down at the rock walls of the Black Canyon, where do you think the oldest rock layers are? Near the bottom, probably. The law of superposition tells us that the layer on the bottom is the oldest, and the layers get younger as they pile up. This is usually true, but not always.
This means that being able to see Precambrian rock here is pretty unusual. Usually the oldest rocks are buried underneath newer rock layers, so there aren’t many places where we can see this Precambrian rock, which was deposited 2 billion years ago. Here, the Gunnison River has carved through the newer rock layers, so we can get a glimpse of both the newer and the older rock.
The walls of the Black Canyon are mostly made of metamorphic rock, and they show evidence of being exposed to extreme heat and pressure. Some of the rock is igneous, formed from magma that pushed its way up into cracks in the Earth’s crust, where it cooled and crystallized. At the next overlook, we’ll look at some examples of each type of rock in the Black Canyon, like schist, gneiss, and pegmatite.
First, though, let’s figure out the geologic time scale. (Walk from overlook to an open space where kids can spread out-maybe in the parking lot or the other overlook?) Divide yourselves into 2 groups, and send one representative over here to pick up your group’s stack of geologic time cards. The goal of this activity is to work as a group to do 2 things: first, determine the correct order that each of these things occurred on the geologic time scale. Second, lay them out, in order and in their correct position, along this line which represents the timeline from when the Earth was created until the present time. You’ll have 5 minutes to accomplish this, starting now. (The timeline should be a piece of rope __feet long, with a card on one end that says “Earth is formed” and on the other end, “Our visit to the Black Canyon of the Gunnison National Park.” Pieces of tape can be wrapped around the rope, marking every million years or so.)
(After the 5 minutes): Look over your timeline. Does everyone agree that the cards are laid out in the right order? Okay, then, I’ll write down the order for each team, and we’ll discuss this at the end. You’ll have a chance to do this again later, and at that point you can make corrections if you decide that the cards aren’t really in order. (Collect the cards and ropes)
Drive to Painted Wall/Chasm View overlook
Now that we’ve talked about the Precambrian, the time before life, let’s briefly touch on a few other important geologic eras. The Paleozoic Era took place after the Precambrian. Paleo means “early life.” Fossils of fish, shellfish, amphibians and primitive reptiles tell us that most of Colorado was flooded by shallow seas during this era. Also, what is now Colorado was covered by two huge mountain ranges, running parallel to each other. They were eroding during that time, due to the shallow sea, and the rocks washed away. That means that part of the geologic story has been wiped out, and we have to fill in the clues from other parts of the southwest to better understand the geology of this area.
The Mesozoic Era followed the Paleozoic. During the Mesozoic Era, the dinosaurs lived and died, birds evolved from reptiles, and the first primitive mammals appeared. The mesas on the North Rim along Hwy 92 in Curecanti NRA reveal some layers of rocks that were deposited in the Mesozoic. At the downstream end of the BLCA, you might see a thin strip of pink or yellow rock. This is the Entrada Sandstone, formed when a massive stack of sand dunes covered most of this region. If you visit Curecanti NRA on your next field trip, you’ll see the Morrison Formation, Dakota Sandstone, and Mancos Shale, layers which were also deposited during the Mesozoic Era.
And finally, the Cenozoic Era, which is the era that we’re living in right now. The Rocky Mountains were formed during the Cenozoic, in an event called the Laramide Orogeny (orogeny, by the way, means “mountain building.”) There was also a lot of volcanic activity from the West Elk and San Juan mountains, forming layers of igneous rock.
So that explains how the rock layers beneath our feet formed, but it doesn’t explain how this great canyon was formed. Does anybody have an idea? Exactly-the water of the Gunnison River has slowly carved the canyon over the past __ million years. The Rocky Mountains are the highlands that serve as the headwaters for the Gunnison River. Geologists believe that the modern Gunnison River became established in its current course 10-15 million years ago. It carved through the relatively soft rocks, like the sedimentary rocks deposited during the Mesozoic time period. Then, about 2 million years ago, the river had carved through all the softer rock layers and hit the hard Precambrian rocks, forced upwards as part of the Gunnison Uplift, which you may have learned about in class. This uplift was a huge block of crust that had been forced upwards during the Laramide Orogeny. So now the Gunnison River is trapped in its own canyon, and its path couldn’t meander into softer rock layers. So, at the rate of one inch per hundred years (the width of 1 human hair per year), the river carved through the rock, forming this canyon. Who can tell me when the Black Canyon reached its maximum depth and stopped being eroded? That’s a trick question, because even to this day, the water of the Gunnison River is eroding the canyon, so it will continue to get deeper as the centuries pass. Dams have been built along the river, so the water isn’t as powerful, but the canyon is still being eroded deeper and deeper, at a slower rate.
Walk from Chasm View overlook to Painted Wall overlook:
Now that we’ve refreshed our memories about the geologic eras, let’s talk about some specific kinds of rock. What are the 3 main categories of rock? Metamorphic, sedimentary, and igneous. How is sedimentary rock formed? Sediments, small particles of sand, silt, mud, and clay, filter down through water and form layers. (show quick demonstration of the bottle filled with sediment, and the layers that form as it settles). Eventually the pressure of the layers or the pressure of the water on top of the layers causes them to harden into rock, albeit a soft rock. Everybody has heard of sandstone (show an example). Pass this around and feel it. It erodes beneath our fingertips, so you can imagine that it might not be too difficult for a powerful river like the Gunnison to erode it fairly quickly. Sedimentary rock isn’t very common at the BLCA, but it’s very common at Curecanti NRA, just 50 miles from here.
How does igneous rock form? Through volcanic activity. There are different types of igneous rock. Extrusive igneous rock is formed when a volcano explodes and the lava is shot out of the top of the volcano, or ash is expelled from the volcano. Intrusive igneous rock forms when magma, or liquid rock, hardens beneath the surface of the earth. Pegmatite is an example of an intrusive igneous rock, so that means that the magma cooled beneath the surface of the earth. (show example of pegmatite) If you look at the Painted Wall, you’ll see stripes of pink rock among the darker metamorphic rock. The pink rock is pegmatite, and when it was in a hot, liquid form, it was squeezed like toothpaste into the cracks of the metamorphic rock. Pegmatite is composed of three main minerals: quartz, feldspar, and mica (show examples of each, and explain that they are the building blocks of pegmatite). Quartz Monzonite is another type of igneous rock at the Black Canyon. It’s a type of granite. (show example)
Last but not least, metamorphic rock. The majority of the rocks in the BLCA walls are metamorphic rock. This type of rock forms when either igneous or sedimentary rock gets buried underneath the Earth’s crust, maybe 6-8 miles deep, and the intense heat and pressure cause the rocks to melt, changing their physical and chemical composition.
Gneiss and Schist are the two main forms of metamorphic rock found at the BLCA. (Show examples) Gneiss was buried deepest, meaning it underwent the most intense temperatures and pressures. It’s hard to tell what the original rock was, but geologists think that the rock around here was originally sandstone, a sedimentary rock. Schists weren’t buried as deeply, meaning they didn’t change nearly as dramatically as the gneisses. So they still look similar to their original rock form. Schists look like a stack of paper. The main difference between gneiss and schist is the thickness of their internal layers, or lamellae (la MEL lee). Gneiss has thick lamellae and schist have very thin, fine layers. Muscovite and biotite mica are minerals found in gneiss (show examples).
***hardness test with feldspar and muscovite mica and schist (flat piece) and pegmatite or monzonite and something that they’re familiar with, like concrete-show difference in hardness of rocks in canyon to demonstrate why the river cuts the canyon more dramatically in the monzonite; compare and contrast with concrete, why concrete erodes quickly in comparison.
Erosion was a very important factor in the formation of the canyon over the past 2 million years. Who can think of an example of erosion and how it impacts our lives nowadays? (erosion along I-70 caused huge landslides that blocked the roads in August, ’05; erosion on trails can make them muddy or hard to follow; erosion along riverbanks may cut someone’s property boundary; erosion on a cliff can make houses fall, like in Southern California in spring, ’05)
TEACHING PROCEDURE/METHODOLOGY (CONT.)
We talked a little bit about erosion, and how that could affect our lives. From something as simple as a trail eroding away into a nearby river to more complex issues like the ground underneath your house eroding away, erosion affects our lives. Engineers need to consider the ground and the rock types when they’re thinking about building a new road. If you were an engineer, thinking about building a new road from Montrose to Denver, would you look for a hard rock base or a softer one to build your road on? A hard one, since it would be less likely to erode, less likely to break down and cause giant potholes. Do you think the roads around here are built on hard rock or soft rock? Actually, the roads and many of the houses in western Colorado and Utah are built on Mancos Shale, which is a sedimentary rock layer, and it’s very soft. That’s why there’s a lot of road repair each year, because the ground underneath the asphalt wears away, breaks down, and becomes unsafe to drive on. (This whole region is covered by Mancos Shale, so it was a decision to either build on top of it and deal with the consequences, or not build roads at all).
But let’s jump back in time again, but this time only one or two hundred years ago. Native American tribes, mainly the Utes, had been living here for many centuries, but theirs was a nomadic lifestyle. They didn’t tend to build roads or permanent houses, because they moved around so much. But when the “white men” started exploring this area, they quickly realized that the lay of the land, caused by the geology, would be very important if they planned to traverse it. And that was their plan. There was competition between a couple of railroad companies to be the first to lay down a railroad track to this region, heading west. They sent explorers to determine the best route, and the geology was extremely important. This canyon made it difficult, but not impossible, for trains to pass through. They ended up using dynamite and a lot of hard manpower to shatter the rock to create a railroad bed. It entered the Black Canyon where the Blue Mesa dam is currently located, and it exited the canyon at Cimarron, along Hwy. 50. The first train passed through in August of 1882.
Another group of people discovered just how hard the metamorphic rock of the canyon walls were-- the farmers who wanted to settle down in the Uncompahgre Valley. They thought it would be a perfect area to grow crops to sell to the high altitude towns where the miners lived, if only they could find a way to irrigate their crops. They realized that all the water they needed and more was located just a few miles away, in the Gunnison River. The only problem was that the river was located deep within the Black Canyon. When you look around the valley today, it looks pretty lush and green, and people have called it “paradise.” So it seems that they discovered a solution to their problem, and they found a way to get water to their crops. Does anybody know what they ended up doing? A group of men, including William Torrence and Abraham Lincoln Fellows, built a tunnel through the walls of the canyon, using dynamite and other explosives back in the early 1900’s. This was very hard labor, and very dangerous. Imagine if you were one of those men, blasting your way through miles and miles of rock. It would be pitch black underneath all of that rock, and it must have worried a few of them, the thought that if they made one wrong move, the rock would cave in on them, burying them alive. But it must have been worth the sacrifice. Water was that important to them, and it still is today. The Gunnison Diversion Tunnel still exists, stretching 5.8 miles from East Portal to the other side of Hwy. 50.
IV. CHECK FOR STUDENT UNDERSTANDING
Did You Know?
At 20 miles long and with 96 miles of shoreline, Blue Mesa Reservoir is the largest body of water in the state of Colorado.