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We visited Arches National Park. The most outstanding natural features of the park are the arches, of course. Over two thousand of them have been identified and catalogued, from a three-foot opening (smallest to be considered an arch) to the 306-foot Landscape Arch.

Click those two thumbnails - they're cropped from larger drawings.
Two other features in the park are also interesting, although much less dramatic: potholes, and cryptobiotic soil. We saw potholes in the Needles yesterday. Cryptobiotic soil is a living ground cover that is the basis of plant life in the high desert. This knobby, black crust is dominated by cyanobacteria, but also includes lichens, mosses, green algae, microfungi and bacteria.
Cyanobacteria, also called blue-green algae, are among the oldest of known life forms. It is thought that these organisms were among the first land colonizers of the earth's early land masses, and played an integral role in the formation and stabilization of the earth's early soils. Extremely thick mats of these organisms converted the earth's original carbon dioxide-rich atmosphere into one rich in oxygen and capable of sustaining life.
When wet, Cyanobacteria move through the soil and bind rock or soil particles, forming an intricate web of fibers. In this way, loose soil particles are joined together, and an otherwise unstable surface becomes very resistant to both wind and water erosion. The soil-binding action is not dependent on the presence of living filaments. Layers of abandoned sheaths, built up over long periods of time, can still be found clinging tenaciously to soil particles, providing cohesion and stability in sandy soils at depths up to 10cm.
Nitrogen fixation is another significant capability of cyanobacteria. Vascular plants can't use nitrogen as it occurs in the atmosphere. Cyanobacteria convert atmospheric nitrogen to a form that plants can use. This is especially important in desert ecosystems, where nitrogen levels are very low.
So there are signs all over, telling visitors to stay on the trails.





This huge rock guards one end of the trail called...

Park Avenue. These geologic skyscrapers tell the story of the Entrada Sandstone.
Entrada Sandstone began forming more than 150 million years ago as tidal flats, desert, and beach deposits. Over time, layers of rock, maybe a mile thick, covered these deposits. Tremendous pressure from these rock layers compressed the buried sand into sandstone and cracked it. Then, erosion removed the overlying rock layers and the Entrada began to weather.
Within the past two million years, erosion of the cracks in the Entrada has left vertical slabs like the rock wall on the right in these photos. These slabs, or fins, are the first step in arch formation.



This drawing from a Park Service brochure explains how arches are formed.

Arches National Park lies atop an underground salt bed called the Paradox Formation, which is responsible for the arches, spires, balanced rocks, fins and eroded monoliths common throughout the park. Thousands of feet thick in places, the Paradox Formation was deposited over 300 million years ago when seas flowed into the region and eventually evaporated. Over millions of years, the salt bed was covered with the residue of floods and winds as the oceans returned and evaporated again and again. Much of this debris was cemented into rock. At one time this overlying layer of rock may have been more than a mile thick.

Salt under pressure is unstable, and the salt bed below Arches began to flow under the weight of the overlying sandstones. This movement caused the surface rock to buckle and shift, thrusting some sections upward into domes, dropping others into surrounding cavities, and causing vertical cracks which would later contribute to the development of arches.

As the subsurface movement of salt shaped the surface, erosion stripped away the younger rock layers. Water seeped into cracks and joints, washing away loose debris and eroding the "cement" that held the sandstone together, leaving a series of free-standing fins. During colder periods, ice formed, its expansion putting pressure on the rock, breaking off bits and pieces, and sometimes creating openings. Many damaged fins collapsed. Others, with the right degree of hardness and balance, have survived as the world famous formations of Arches National Park.

Several of Arches' landmarks are seen here. The large formation at right wasn't identified on the park map. At center, we see the Tower of Babel and the Organ. Left of that is Sheep Rock, and then the Three Gossips. To the Southeast (second photo), the La Sal Mountains are visible here, as they are from many places within the park.

Here are closer views of the Three Gossips and of Sheep Rock. Sheep Rock is thought to be the remnant of an arch whose crown has already fallen off. From this viewpoint, it's the right leg of the crumbled arch.

This vast area was once covered by extensive sand dunes. 200 million years ago, winds from the northwest carried tons of fine-grained sand into this area, creating an immense desert. Over time, the sand drifts were covered by other layers of sediment, compressed, and cemented by quartz and calcite into Navajo Sandstone. Erosion has since washed away the overlying layers, exposing these "petrified" dunes.

Balanced Rock, from a distance and closer in. In the distant photo, Balanced Rock is the second major structure from the left. You can also see another rock above a butte on the right, which also looks like a balanced rock. This second rock is visible from many parts of the park.



Balanced Rock.


Here and in many other places, part of the trail is on slickrock. The Park Service uses small cairns to mark the trail, which would otherwise be invisible.



Here's another look at the "other" balancing rock, seen while walking around Balanced Rock.


On the spur road from Balanced Rock, a visitor drives by the Garden of Eden, Cove Arch and the Parade of Elephants on the way to the North and South Windows.

Another view of Cove Arch, just right of center in the photo. This arch is in an area called Cove of Caves; several of the caves are seen here, too.
Caution: this photo is very wide (there's a smaller version here).




Turret Arch, near the Windows.


Scenes from a walk around the North and South Windows.

 

It's very windy around the North and South Windows. The trees are eroded faster than the rocks, of course, but they manage to survive. (The last tree was actually on the road from Balanced Rock to the Windows.)


About halfway around the loop trail, we were rewarded with this view of the South and North Windows, seen from the East in mid-afternoon.
This photo is very wide (there's a smaller version here).


The view from Panorama Point includes the La Sal Mountains, plus all the things we had just seen in the Windows Section.



This cave is an arch in progress.



Double Arch.


Pothole Arch. We didn't see the pothole on top. It was hot.

Most of the Arches Park is Salt Valley, like this view seen on the road from Panorama Point to Delicate Arch.

Caution: this photo is very wide (there's a smaller version here).

John Wesley Wolfe built this homestead for his ranch here about 1898, and lived here for ten or fifteen years. While he was here, he and his sons found the Delicate Arch on their property. He moved back to Ohio, but the Park Service has kept his cabin as a reminder of the harsh life these people lived.

There are petroglyphs near the Wolfe Ranch. too.

We started up the incredibly steep trail to Delicate Arch, one of the park's most memorable scenic attractions. This arch appears on the license plate of a lot of Utah cars, and is usually the most memorable sight associated with the park. It's also in this picture from the NPS web site.
Because of its distinctive shape, this arch has also been called "Cowboy Chaps" and "Old Maid's Bloomers." Carved in Entrada Sandstone, this free-standing arch is composed mostly of the Slick Rock Member. On top is a five-foot-thick layer of the Moab Tongue. A remnant of an ancient fin, the arch today has an opening 45 feet high and 33 feet wide.

But it was too steep, and much too hot, so we contented ourselves with the striking views we got from the trail until we were about two-thirds the way to the top.


This is a distant view of Delicate Arch, from a viewpoint about a mile away that's easily reached by car.

Arches usually form slowly, but quick and dramatic changes do occur. In 1940, a large boulder suddenly fell out of Skyline Arch, roughly doubling the size of the opening.

There are no trails in the Fiery Furnace, the footing is poor, and the area is laced with dead-end canyons. So the Park Service restricts access to 3-hour guided tours or by getting a hiking permit. We settled for the view from the trail head.

 

Trees and rocks at the Devil's Garden trail head and picnic grove.


on to Sutter Creek

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