Tuesday, April 21, 2009

(Almost) Backyard Geology: A Field Trip

If your thought process is like mine was before I enrolled in a couple of geology classes this semester, your view of the Earth and its history is fairly simplistic: The surface of the Earth, including its mountains, basins, and other geologic formations, is the same today as it has always been (except, of course, for the addition of any man-made features, like reservoirs or irrigation ditches). Dinosaurs are long gone, having lived "way back when" wherever there existed tall palm trees, colorful sunsets, and tiny mountains in the distance -- which, by my logic, would be the same locations that today feature tall palm trees, colorful sunsets, and tiny mountains in the distance.

How wrong I was! Looking back, it's all a bit comical. I think I must have colored one too many over-simplified dinosaur coloring books as a child.

This semester I've learned dinosaurs existed very near where I live, in Pueblo, Colo. I also learned where I live was previously underwater. Remnants of dinosaurs and sea creatures, as well as some colorful, fascinating geology, are located within a short drive of my house, as evidenced by this field trip.

Please note that I took all pictures used in this blog, including the blog's title/header picture (the Cuelebres Range of the Sangres and Goemer Butte, taken from the outskirts of La Veta). Oh yeah -- I didn't take the photo of myself. My husband took that photo. But I took the rest. :)

We begin our trip at my home in Pueblo West, Colo., just several miles away from the intersection of Highway 50 and Purcell Boulevard.

From my backyard: The Spanish PeaksMy land has some great geologic scenery. All you have to do is stand on my back patio and skim the horizon from south to north. Here are the Spanish Peaks. They are the remaining necks of twin, Tertiary-age volcanoes that pushed through Cretaceous-age sedimentary rock, or rock formed by the consolidation of sediment or precipitation of minerals from a liquid substance. The volcanoes used to be larger, but the remainder eroded away, leaving what you see today.

From my backyard: The Sangre de Cristo MountainsNext come the Sangre de Cristo Mountains, which are visible behind the darker Wet Mountains (far right) and below the white clouds (nearly as faint). You can see the Sangres by just rotating a bit to your right, or northwest. The entire range actually extends from Salida, Colo., into New Mexico! The northern most end of the range, what you see here, is made of Precambrian igneous and metamorphic rocks. (Igneous rocks are formed when molten material cools. Metamorphic rocks are formed within the Earth as preexisting rocks are reformed by heat and pressure.) The majority of the range, however, is composed of Permo-Penn sedimentary rocks, which are actually reddish-colored sandstone rocks. Early Spanish settlers noticed the red tint, especially while the sun was setting, and consequently named them the "Sangre de Cristos," which means "the blood of Christ" in Spanish.

From my backyard: The Wet Mountains If you rotate to the right, or northwest, a bit further, you'll find the Wet Mountains, noticeably darker than the Sangres and the Rockies. The Wets are a small range composed of Precambrian granite. (Granite is an igneous rock that mostly consists of quartz and feldspar.)

From my backyard: Pikes Peak and the Front RangeAnd finally, rotating to the furthest point northwest (mostly north), you'll see Pikes Peak and the Rocky Mountains. Most of the Front Range is composed of gneiss, a metamorphic rock with granular crystals situated in usually wavy layers, and the Front Range is bounded by vertical faults on both the east and the west. (A fault is a surface along which rocks have fractured and moved.)

Not a bad geology lesson for having not even moved from my backyard!

Our first official field-trip stop will be Canon City's Skyline Drive. On the way we'll stop at the Dinosaur Depot Museum in Canon City. To get there, take Highway 50 from Pueblo West for 28.9 miles. The museum is on your left. Its official address is 330 Royal Gorge Boulevard #330. I was told to simply "turn at the dinosaur" once you enter Canon City. If someone tells you this, you're likely to be a bit confused, as you will see a dinosaur on your right in Canon City. There you'll find some great information about Canon City's dinosaur fossils and tourist attractions, but you won't find the Dinosaur Depot. So, to put it simply, turn left at your second dinosaur.

Canon City's Dinosaur Depot: The Apatosaurus Femur & IHere I am sitting on top of a 1,100-pound Apatosaurus femur inside the Dinosaur Depot. (Yes, the museum staff invites and encourages visitors to sit on top of it!) If you're interested in learning more about the geology of the Canon City area and/or the Front Range, visiting is an absolute must. Inside is the world's most complete stegosaurus skeleton, an actual paleontology laboratory, fabulous exhibits explaining the Bone War history and interesting geology of the Garden Park Fossil Area, an upstairs filled with hands-on activities, and a great gift shop that sells, among other things, two guides you'd be silly not to purchase: Self-Guided Tour of the Skyline Drive Dinosaur Tracks and Self-Guided Tour of the Garden Park Fossil Area, both "published" by the museum. They appear unassuming and sure aren't anything fancy, but you couldn't ask for better guides to the areas we're about to explore. Plus, they're only $1 and $2 respectively.

We'll now head to Skyline Drive, also in Canon City. Jump back on Highway 50 by turning left from the museum. (You'll be heading west.) Just 3.4 miles later you'll find the entrance to Skyline Drive on the right shortly after you drive past the Razor Ridge Trading Post. Be careful -- it's a steep drive!

Skyline Drive: AKA the Dakota HogbackHere we are on top of Skyline Drive, a fancy name for the road on the Dakota Hogback. The actual road, seen here, lies on the ridge of some Dakota Sandstone. For the most part, the hogback continues southward past the Colorado/New Mexico state line.

The View from the DriveLooking a little further west from the hogback we glimpse a spectacular view of the Wet Mountains and the Gore Hills, as well as the valley between the hogback and the mountains.

Unique UpliftBut the real heart of Skyline Drive -- or what draws most visitors -- is located just before the two previous pictures. The hogback of Skyline Drive serves as the west, north, and northeast rim of the Canon City Basin, located to the east (or right, in this picture). What is today Canon City was, during the Cretaceous Period, the bottom of the Western Interior Seaway: a warm, relatively shallow sea that extended all the way from the Gulf of Mexico to the Arctic Ocean! But back when Canon City was an ocean floor, neither the Canon City Basin or Skyline Drive/the Dakota Hogback existed. The sandstone walls of the basin, like the one seen here, were later uplifted an at obvious angle by the Rocky Mountain Uplift. Take a look at the uplifted segment at the very left of the picture. The very bottom layer is the Plainview Sandstone, and the upper portion consists of the Glencairn Member.

"Bronto Bulges"
Fascinating, huh? It gets better. Continue walking back in the direction you came from, staying close to the uplifted rocks. Stop when you arrive at the displays explaining Skyline Drive and look UP! What you're looking at are some of the coolest trace fossils -- or trails, tracks, or burrows left by a moving animal -- you'll ever see! During the Cretaceous Period the Glencairn Member did not exist, but the Plainview Sandstone was being formed -- and it wasn't uplifted like it is now. You're currently standing at the location of a Cretaceous Period estuary -- or a wet area where a fresh-water river meets a salt-water ocean. The area was muddy, and just like your shoes make prints in the mud after a rain storm, the dinosaurs left tracks as they walked westward. Being so close to shore, sand, plant material, and other debris were washed into the imprints, leaving casts. Then, as previously mentioned, the sandstone was uplifted by underground forces. What you're looking at is the BOTTOM of the sandstone, the BULGES left as the dinosaurs walked. The view is as if you were standing below the land the dinosaurs walked on looking up!

A Theropod TrackHere's a close-up of one track. It's the footprint of a Theropod, a carnivorous dinosaur. Credit goes to Canon City resident William Kurtz for realizing these odd bulges were actually extremely unique trace fossils. I'm sure folks had for a long time wondered what they were. He was the first to figure it out -- or at least the first who didn't keep the discovery to himself.

More Trace TracksHere are some additional dino tracks. The track at the bottom left, I believe, is also from a Theropod. At Skyline Drive you'll find entire sets of front and back feet belonging to the same dino, the tracks of one dino intersecting another dino, and even burrows and root and log imprints, if you look close enough.

If you keep following Skyline Drive, it will spit you out not far from the Dinosaur Depot Museum, where you started. At the end of Skyline Drive, turn right onto 5th Street, then left onto Highway 50. Now follow Highway 50 in the opposite direction, back toward Pueblo. Turn left at your fourth traffic light (at Burger King) onto Reynolds Avenue. After one block, turn right on Field Avenue. Keep on Field Avenue for another six miles approximately. You'll find yourself in the Garden Park Fossil/Red Canyon Park area -- our next stop.

Red Canyon Park
It's not a long haul from Skyline Drive to the Garden Park Fossil Area, which includes the Marsh and Cleveland quarries, and the nearby Red Canyon Park, pictured here. While I'd hoped to nose around in the quarries, they were temporarily closed. But the geology of the area is fascinating, nonetheless. While it may be difficult to picture dinosaurs roaming around the area, they sure were -- and in large quantities. The area is considered a hot bed for dinosaur bones and other fossils. Excavation began in the late 1800s and served as the stage for the "Great Dinosaur Race," the "Bone Wars" between Edward Drinker Cope and Othniel Charles Marsh, both professors and paleontologists. Unlike other dinosaur bone hot spots, such as Dinosaur National Monument in Colorado/Utah and Como Bluff in Wyoming, the entire Morrison Formation here produces fossils from top to bottom, whereas most other areas only produce fossils near the middle of the formation. Excavators have discovered here 20 brand new genera and many more new species -- fish, turtles, lizards, crocs, dinos, and some relatively small mammals. Clams, snails, and shrimp have also been discovered here, and the Bell Ranch Formation, just below the Morrison, even produced one of the oldest ray-finned fish fossils to be discovered. Many dino specimens found here are complete, or near complete. The dinos discovered here include the Stegosaurus stenops, Apatosaurus, Allosaurus, Ceratosaurus, Diplodocus, and Othnielia rex. Specimens discovered here are located at museums around the U.S. and the world, including the Smithsonian in D.C., the Denver Museum of Nature and Science, and museums in Europe.

Sandstone and ClayHere we are just a bit down the road on our way back to Canon City. In the background we see the Quarry Sandstone of the Morrison formation, but notice the red surface of the road. The red swelling clay was deposited in the area as volcanic ash shortly after the deposition of the sandstone in the background.

We're now headed to the Pueblo Reservoir, or Lake Pueblo. Reverse the aforementioned directions until you're back on Highway 50. Head back toward Pueblo. You'll follow Highway 50 for about 22 miles before making a right on Thatcher Avenue. Follow this road for three miles, then turn right at the reservoir.

Wet Then, Wet NowThough the Pueblo Reservoir is man-made, a certain portion of the body of water retains its geologic history. According to the Colorado Department of Natural Resources Website, students from as far away as Virginia have come to study the geology of the lake.

Calm? Waters
During the Cretaceous Period, the land of the Pueblo Reservoir was, in a major way, as it is now: underwater, in the Western Interior Seaway! The seaway left many stratified rock layers and so many animal and plant fossils, both trace and actual!

A Pretty Pattern Many cool, slate-like limestone rocks line the western edge of the reservoir and contain neat Cretaceous fossils. Ignore the shadows, here, and look at the raised imprints on the rock. They appear to be coral or some kind of seaweed.

Trapped by SedimentThe Pueblo Reservoir actually sits atop the Niobrara Limestone of the Cretaceous Period. (Limestone is a sedimentary rock that mostly consists of calcium carbonate.) According to the Roadside Geology of Colorado, this limestone is full of shellfish fossils. Here is a fossil I found in one of the larger, slate-like limestone rocks. I broke it into smaller pieces. This fossil is typical of Cretaceous brachipods, marine invertebrates with shells divded into two halves. According to a Canon City Basin Rock Column chart I was given at the Dinosaur Depot, it might be a Mytiloide.

A Big ClamHere is another fossil I found in a similar, slate-like piece of limestone in the shallow waters of the lake. Most of the surrounding rock easily broke away when I (purposely) dropped it. (I'm not all that technical when it comes to fossil recovery. I probably should be!) This large clam is nearly bigger than my hand (though I have small hands) and is completely solid. Though this could just be the shell filled in with sediment, I think the remains of the rest of the clam are probably preserved within it. It looks an awful lot like the Cremnoceramus sketch on the aforementioned chart, but Roadside says the fossils of the Inoceramus, a large clam with a corrugated shell, are very common in the Niobrara Limestone around Pueblo. I'm not sure what it is exactly, but it's cool!

Hopefully you've had a great time on this short field trip. It's fascinating to think I live exactly where fishes used to swim and near where dinosaurs used to roam. If only I could start excavating in my backyard. I would, but I think my husband would kill me!


Guide to the Geology of Colorado. by Andrew M. Taylor. (C) 1999. Published by Catract Lode Mining Company, Golden, CO.

Roadside Geology of Coloraod. by Halka Chronic and Felicie Williams. (C) 2002. Published by Mountain Press Publishing Company, Missoula, MT.

Geology of Colorado Illustrated. by Dell R. Foutz. (C) 1994. Self published.

Earth System History. by Steven M. Stanley. (C) 2005. Published by W.H. Freeman and Company, New York, NY.

Self-Guided Tour of the Garden Park Fossil Area. by Donna J. Engard and Emmett Evanoff. No copyright date. Published by the Garden Park Paleontology Society's Dinosary Depot Museum, Canon City, CO.

Self-Guided Tour of Skyline Drive Dinosaur Tracks. by Donna J. Engard and Emmett Evanoff. No copyright date. Published by the Garden Park Paleontology Society's Dinosary Depot Museum, Canon City, CO.


1 comment:

  1. Erin, this is absolutely fascinating! Thanks so much for posting!