Grosvenor Arch

Grosvenor Arch

Grosvenor Arch is located in the northwestern corner of Grand Staircase-Escalante National Monument in southern Utah. It is unique in that it is actually two sandstone arches towering 150 feet above the ground.1 The larger of the two arches is nearly 100 feet in diameter.2  The arch was named for Gilbert Hovey Grosvenor who was the president of the National Geographic Society and would become the first full-time editor of National Geographic Magazine.3

The arch is accessible from either the north or the south via Road 400, also known as Cottonwood Canyon Road. It is ten miles by car from the nearest paved road. When you reach the small parking area, there is a sidewalk that will take you almost right to the base of the arch.

Water (and to a much lesser extent, wind) persistently carved away at the landscape to form this structure. The arch is formed in yellow Henrieville Sandstone from the late stages of the Entrada Formation. The capstone layer is formed of darker Cedar Mountain from between the underlying Morrison and overlying Naturita Formations, and Dakota Formation sedimentary rock.4

1. http://www.utah.com/nationalparks/bryce_canyon/grosvenor.htm
2.  http://www.utah.com/nationalparks/bryce_canyon/grosvenor.htm
3. http://en.wikipedia.org/wiki/Gilbert_Hovey_Grosvenor
4.  http://www.digital-images.net/Gallery/Scenic/Southwest/Utah/GrandStrcase/GrsvnrArch/grsvnrarch.html

Dinosaur Wrangler

A white government issue truck speeds along the Cockscomb leaving a lingering trail of dust, the occupant seemingly uninterested in the stunning scenery that surrounds him. Another truck pulling a trailer creeps along, two sinewy cowboys dressed in Wranglers scan the landscape for stragglers, a Coors beer rests in the console, their cigarettes glowing a fiery red match the horizon as they are swallowed up in the dusk and another invisible valley. An unsuspecting car with California plates traveling towards Kanab crosses the plateau. The occupants probably unknowing that they have left Bryce Canyon National Park are unaware of the rich, biodiverse, paleo-treasure that lies to the east as they marvel at the rugged outcropping of rocks formed by the differential weathering of a monocline caused by a faulting in the basement rock during the Laramide Orogeny.

The wind carries the fine dust as it settles across the expansive dry landscape. The desert somehow becomes more dramatic with the knowledge that the region was once an area of moist peat swamps and rivers flowing into the Western Interior Seaway from the Sevier Highlands millions of years ago during the Cretacious Period. The Kaiparowits Plateau has not only seen a history of extreme climates but is also a plateau and a basin at the same time. The area to the east was uplifted during the Laramide while the Kaiparowits Basin was folded down. Later the area erosion of the Colorado River left behind a high plateau. This unique feature mixed with the rich paleoclimate created a perfect storm of sorts for dinosaur fossils and the occasional pristine preservation of a biological microcosm. Plants and animals frozen in place create a mysterious intrigue that pulls you back for more, a thirst to understand their origin, their life and their demise.

The amount of new species and understanding of the history of our earth that has come out of the Kaiparowits is just the tip of the iceberg. The Kaiparowits Plateau or Basin depending on your area of study, is on the forefront of humankinds understanding of paleontology of Late Cretaceous dinosaurs. A white government truck parks on the edge of one of the seemingly infinite outcrops of the Kaiparowits. A jackhammer, shovels, pickaxes, probes and paintbrushes wait for hands to uncover just a few more feet and maybe the skull of a new species.

-Albert Behling

CSI Cretaceous

While we were out digging up dinosaur bones Dr. Alan Titus told us that there is sometimes still evidence in the bones and around the bones of how the dinosaur had actually died.  I  (being a future forensic scientist) found this fascinating. I didn't realize that the same process that we use today to solve crime could solve the mysteries of the dinosaurs. It never occurred to me before that the way  dinosaurs died could be determined in the same way that we solve crimes and events of today!

Sometimes there are bones that have teeth marks in them which tells you that the dinosaur was attacked.   The pattern of teeth marks may help determine if this was the cause of death. The other fossils that are found around the bones and the type of rock that you find the bones in can tell you about the environment that the dinosaur lived in.

The Hadrosaur that we dug up was interbedded with clams, fossil wood, leaves and turtle shell.  The rock was also very clay rich. This told us that it was a probably a lake or pond on a floodplain. We also found a Tyrannosaurid tooth next to the bones.  Maybe our hadrosaur had been attacked by the tyrannosaurid.   More work needs to be done before we can determine this.

Float Mapping

A few of us were able to go out looking for dinosaur bones close to the dig site. At first all we knew was to look close to outcroppings on the sides of the hills, but as we explored and searched the area we noticed patterns in the pieces of bone that we were finding. We would find pieces that looked extremely weathered in the small washes and

at the bases of hills. Once we found these pieces we would generally find more pieces higher up the hill above where we found the first. As we moved up the hillside the pieces we would find appeared less and less weathered until we wouldn't see any pieces at all. When we stopped finding bone we would brush away at the hillside where the last piece was found and sometimes find the source of where the bone fragments were coming from, usually from a bigger piece of bone still partly covered by earth. Float Mapping usually refers to finding loose rock below its source, but we were able to apply the same principal in finding where loose bone fragments came from. This same process is how many of the dinosaur bones are found in the Grand Staircase.

Hoodoos

HOODOOS

On our beautiful drive through the Grand Staircase National Monument to Camp K, we passed by some pretty cool structures, such as monoclines, hogbacks, arches, and my favorite, hoodoos!  Hoodoos are found all over High Plateau region of the Colorado Plateau.  They appear to have a "totem pole" type body shape, due to the erosion patterns of alternating hard and soft layers underneath a hard cap-like layer, acting as a roof.  For example, soft mudstone or poorly cemented sandstone covered by a protective layer of well-cemented sandstone, limestone, or basalt.  Further erosion of the softer layers causes the cap to be undercut, eventually falling off (balancing rocks), and the leftover cone is then quickly eroded (NPS.org).  This is a great example of differential erosion.  

Hoodoos are found mostly in hot, dry, desert areas.  On our field studies trip last spring to the Moab area, we saw tons of them, especially at the Fiery Furnace!  Interesting fact: minerals deposited within the rock give them the appearance of different colors throughout their height.  In this image, the iron oxide makes the rock reddish.

Information found from the National Park Service's Bryce Canyon website says that Hoodoos can be eroded when winter snow melt seeps into the cracks and freezes at night, called frost wedging.  When the water freezes, it expands almost 10 percent and pries open cracks in the rock, making them even wider; similar to how a pothole forms in a paved road.  Geologically speaking, they live a short life; their average rate of erosion is 2-4 feet every 100 years.

Information from National Park Service's webpage: http://www.nps.gov/brca/naturescience/hoodoos.htm

Pictured above:  Hoodoos found outside of the visitor center at Red Canyon on Rte 12 west of Bryce Canyon.   They are in the Claron Formation.

How can you tell the difference between a dinosaur bone and a piece of petrified wood?

I have learned the value of being able to properly distinguish dinosaur bone from petrified wood. While on our field trip I happened across what I thought was a large round piece of petrified wood. So thinking that it was just another chunk of cretaceous wood, I decided to see just how big it was. Before doing this however I conducted the “lick test” to make sure it was not bone. The reason the “lick test usually works is because bone is porous, this allows the moisture from your tongue to be absorbed into the bone. This causes your tongue to stick to the bone. Wood is not porous so it does not have the same affect. After doing this test I determined that's what we had found was wood. I soon learned that this test is not always accurate. It turns out what I thought was a large piece of tree was actually a Hadrosaur femur. The most sure fire way to find out if something is bone or wood is to ask a paleontologist. If you have any hunch that you have found a bone the best thing to do is take its GPS location and leave it exactly how you found it.    

The Kaibab Monocline

Our class was able to meet with Dr. Alan Titus in the Grand Staircase National Monument. We helped dig up some real dinosaur bones. It's not every day you find yourself digging up something you've seen only in the movies and natural history museums. 

We were asked to give a brief explanation of something we learned on the field trip. I have chosen a geological feature known as the East Kaibab monocline.  A monocline is a single bend (mono) of rock strata. (picture below)

The East Kaibab monocline dips from west to east and runs north to south. The formation of the monocline is due to a west dipping reverse fault. This fault lays in the Precambrian rock beneath the newer folded Mesozoic and Paleozoic Rock. The hanging wall of the reverse fault moved up and pushed up overlaying rock with it. The foot wall moved down allowing the rock above to settle. Over millions of years the Mesozoic and Paleozoic rocks has slowly been eroded down into jagged hogbacks and deep slot canyons. The weather resistant sandstone forms most of the protruding hogback features. East (picture looking south) of the Navajo and Dakota sandstone the less erosion resistant Tropic Shale (Caleb Franks is standing in) forms a valley that parallels the monocline. (picture below)

 

Crevasse Splays

I can think of few events in my life that can compare to digging up dinosaurs with Alan Titus. Not that there haven't been fantastic moments in my life, but digging up dinosaurs with a busy paleontologist is just kind of unique experience that not a lot of things compare to. That just goes to show how incredible geology really is.

While working with Alan, digging up what we think to be a Hadrosaur, in the Grand Staircase National Monument, I was told about an interesting event that happens along rivers called a crevasse splay. Some of the dinosaurs were found in crevasse splay deposits. My interest was peaked and so I will attempt to paint a picture for you.

Imagine that it is the rainy season of the year. The river's banks are filling and soon the water will overcome the levees. It isn't anything new to the area seeing as this is a well established meandering river. As you are overlooking the river, you see a weak point in the levee begin to give to the weight of water against it. All of the sudden the river breaks through at that point. It starts out small but rapidly grows into a side channel. The swift moving water from the river cuts a ravine in the soft levee sediment. As you look past that point where the levee broke, you see a Hadrosaur grazing in the flood plain. You call out to it to move out of danger but it is too late. The water overtakes the dinosaur and it disappears from view. Soon you can see the sediment carried from the river, through the crevasse, and out into the flood plain settling into a fan shape. You, however, don't see the unfortunate Hadrosaur.

This is an aerial  view of a crevasse splay. One much like an unsuspecting Hadrosaur could get caught up in. Turns out that crevasse splays are fantastic places to find well preserved dinosaurs. However, sometimes the river's cut bank will erode far enough into the flood plain to scour out buried dinosaurs and other fossils. Pretty cool stuff, right?