The Sound of Geology
One of our most visited National Parks averages more than a half-million visitors per month in the summer, visitors who flock to see massive sandstone cliffs of cream, pink, and red that soar into a brilliant blue sky, and it’s main feature, a glorious canyon carved by an unassuming yet powerful river.
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Zion National Park is located along the edge of a region known as the Colorado Plateau. The rock layers have been uplifted, tilted, and eroded, forming a feature called the Grand Staircase, a series of colorful cliffs stretching between Bryce Canyon and the Grand Canyon. The bottom layer of rock at Bryce Canyon is the top layer at Zion, and the bottom layer at Zion is the top layer at the Grand Canyon.
Zion was a relatively flat basin near sea level 240 million years ago. As sands, gravels, and muds eroded from surrounding mountains, streams carried these materials into the basin and deposited them in layers. The sheer weight of these accumulated layers caused the basin to sink, so that the top surface always remained near sea level. As the land rose and fell and as the climate changed, the depositional environment fluctuated from shallow seas to coastal plains to a desert of massive windblown sand. This process of sedimentation continued until over 10,000 feet of material accumulated.
Mineral-laden waters slowly filtered through the compacted sediments. Iron oxide, calcium carbonate, and silica acted as cementing agents, and with pressure from overlying layers over long periods of time, transformed the deposits into stone. Ancient seabeds became limestone; mud and clay became mudstones and shale; and desert sand became sandstone. Each layer originated from a distinct source and so differs in thickness, mineral content, color, and eroded appearance.
From Zion to the Rocky Mountains, forces deep within the earth started to push the surface up. This was not chaotic uplift, but very slow vertical hoisting of huge blocks of the crust. Zion’s elevation rose from near sea level to as high as 10,000 feet above sea level.
This uplift gave the streams greater cutting force in their descent to the sea. Zion’s location on the western edge of this uplift caused the streams to tumble off the plateau, flowing rapidly down a steep gradient. A fast-moving stream carries more sediment and larger boulders than a slow-moving river. These streams began eroding and cutting into the rock layers, forming deep and narrow canyons.
Since the uplift began, the North Fork of the Virgin River has carried away several thousand feet of rock that once lay above the highest layers visible today. The Virgin River is still excavating. Upstream from the Temple of Sinawava the river cuts through Navajo Sandstone, creating a slot canyon. At the Temple, the river has reached the softer Kayenta Formation below. Water erodes the shale, undermining the overlaying sandstone and causing it to collapse, widening the canyon.
One of the most popular areas of the park is where this transition happens. Everyday visitors walk the paved riverwalk trail, while the more adventurous head upstream, hiking through the water of the narrows. Here, geology is constantly in motion.
Unlock the hidden geologic mysteries of river stones with Park Ranger Robin Hampton as she reads an article written by Park Ranger Barb Graves for the park’s Nature Notes.
The Secret Life of River Stones
If you’ve spent any time on the riverwalk trail, then you’ve certainly met the unofficial park mascot – the rock squirrel. In their home, animals like the rock squirrel encounter an overabundance of human contact on a daily basis. Having been on the River Walk trail a few times myself, I can tell you the rock squirrel is the king of the castle here. If you even consider taking out that Nature Valley bar, they will come for you and take it. They also have zero issues rooting through your bag if you set it down. You’ll often see people snapping pics and oohing and aahing over these “cute” little squirrels.
But in our this next audio clip narrated again by Park Ranger Robin Hampton, from an article written for the park’s Nature Notes by Park Ranger Amy Gaiennie, we learn a little bit more about the “Misunderstood Rodent.”
Perhaps a bit of that will keep you from putting your finger near a rock squirrel.
The Virgin River winds through the park and beyond into the gateway town of Springdale, where you can find all sorts of lodging and dinging options for a visit to Zion. There are two campgrounds in the park, the Watchman, which has electric and water, and can accommodate large RVs, is reservable 6 months in advance, and the neighboring South Campground features primitive sites and can be reserved up to two weeks in advance. The spectacular virgin river flows through both campgrounds.
It’s best to stay in the park if you can, because the parking lot fills nearly every day, and you can’t just drive through the canyon, you have to take the park’s shuttle system. If you do stay outside, there’s another shuttle that runs through the town of Springdale, but you’ll have to pay about $20 to park.
See all Zion National Park Audiocasts here.
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Links to some of the resources we used and the website links we mentioned in this episode.
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