GEOSC 10
Geology of the National Parks

Bryce Canyon National Park

Bryce Canyon National Park

 

Left: US Map with Bryce Canyon National Park marked; Right: View of Bryce Canyon
Left: A map of the U.S. with Bryce Canyon National Park marked in Utah. Right: A view of Bryce Canyon National Park, Utah, looking into the canyon from the rim.
Credit: R. B. Alley © Penn State is licensed under CC BY-NC-SA 4.0

Bryce Canyon is a fairyland. Pillars, spires, and minarets, seemingly fragile and toy-like when viewed from the rim, tower far above the hiker who descends into the “canyon,” which is a bowl carved out of the edge of a plateau. The morning sun, bouncing off the pink and pastel walls, casts a rosy glow on everything and everyone in the canyon. Gnarled trees cling to high slopes, their root structure exposed by erosion but somehow holding and nourishing the twisted branches. The old settler Ebenezer Bryce called the scenery of this tributary of the Paria River “a hell of a place to lose a cow,” but almost everyone who followed him has had a kinder assessment.

The main pink rocks of Bryce are a mixture of limestones, shales, and some coarser sandstones and conglomerates, deposited in a lake or a series of lakes, and together are known as the Claron Formation or the Bryce Limestone. (Geologists studying regions have found it useful to give specific names to recognizable bodies of rock, with the names taken from geographic locations. Because the criterion for a new name is the ability to recognize a unit in the field, some careful observers like to subdivide, and others like to lump, so there is often slight disagreement as to which name is most appropriate.) These Bryce rocks are from the early part of the Cenozoic, roughly 40 million years ago. The rocks record a generally wet time shortly following the uplift of the land from a shallow seaway, and before continued uplift led to the high plateaus of today, and climate change dried the surroundings to the dry climate now at Bryce.

Some of this story is told in the rocks of Bryce. The rest is told nearby. Northeast of Bryce in central Utah, the rocks record the gradual transition from undersea to terrestrial. The growth and erosion of mountains to the west are marked by the appearance and then disappearance of coarse braided-stream deposits. These were replaced by slower streams, then by lakes, then another pulse of river sediments, and then the great Green River lakes that spread from Bryce to Wyoming and that record a wet, warm time in the west.

Geologists love to tell stories like this one. The seas came in, the seas went out, the mountains rose, and the mountains were eroded. Such stories are useful because they often include chapters such as “The oil formed here and migrated there, and was trapped in those rocks, and we can drill into it this way and get rich." (Or, the stories may involve gold, or lithium, or rare earth elements, or clean water, or other things we need). Such stories tell us much about the stability of the Earth’s climate. And the stories are interesting to many people. But how do you read such stories, and gain confidence in them? One way to find out is to major in Geosciences and spend the next three years learning to do so professionally—in case you’re interested, talk to us! But if you’re excited about the great career prospects in your current major of theatre or philosophy or whatever else you are studying, at least read over the next few sections and you’ll get a brief sketch of geological techniques and what they tell us.

We saw at the Badlands that weather attacks and breaks down rocks, and we saw at the Tetons, in Canyonlands, and elsewhere, how the loose pieces are transported. The processes of weathering and erosion produce new minerals from old, produce small pieces from big ones, produce dissolved salts, and move these around on the surface of the Earth. Eventually, these materials end up somewhere. The pieces that are derived from older rocks and the deposited we call sediment. Sediment may be deposited on the bottom of a sea, on the flood plain of a river, or at the end of a glacier. Sediment may stay for a while and then be moved on. If it stays for too long, it may be hardened.

There is no magic in making rock from sediment, nor is there an abrupt line separating the two. Many processes slowly transform loose pieces into pieces stuck together. If you don’t believe that loose pieces get stuck together, go to an old house and try to remove some piece of plumbing without using a big wrench, or try to get pieces off an old bicycle without a big wrench. If you don’t have the time, trust us—people make big wrenches for a good reason! Nature does cause changes that bond things together in many cases.

The weight of additional material deposited on top of the sediment layer will squeeze it, forcing grains together and pushing water out. The resulting material is harder than what was there before. Continued squeezing and heating as sediment is buried (remember that the Mississippi Delta is many miles thick) produce rock from this sediment and may eventually change these sedimentary rocks to metamorphic rocks. The clays in sediment change into different clays and then into other things as the cooking proceeds (just as flour and water and yeast make cookies in the oven), and as the crystals of the new minerals grow, they tend to wrap around each other and get “woven” together in an interlocking mass, so they are hard to separate.

Groundwater circulating through sediments will dissolve minerals in some places and precipitate them in others, in response to subtle changes in temperature, pressure, or chemistry. We saw that there is dissolved rock in Spring Creek water, and in all other waters. If you have “hard” water, of the sort that causes people to buy water softeners, that means the water has a lot of dissolved rock and especially dissolved limestone. The white deposit that builds up on drinking glasses in houses with hard water is not soap scum but rock, very similar to stalactites in a cave. A lot of the sticking-together of plumbing pieces is linked to minerals precipitated from hard water. What happens in your house can happen in nature, where the precipitate serves as a cement that binds particles together. This cementation, together with the compaction from squeezing and the recrystallization from heating and changing clays and other minerals, slowly turns loose sediment into sedimentary rock. Sometimes, rocks are made entirely of hard-water deposits—stalactites are an example, but so are the salt deposits containing borax and other materials left in the bottom of Death Valley when the water that runs down from the nearby mountains quickly evaporates. Rocks made entirely of precipitate are also called sedimentary rocks.

Take a Tour of Bryce Canyon National Park

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Bryce Canyon National Park
(Provided by USGS)