Tourist Trek to the American Southwest
A well known nineteenth century musical comedy features the Mikado, a head of state who knew what he wanted. He wanted to execute people he did not like. Indeed he had a little list of these proposed victims. One of the most amusing solos in the musical is his refrain
- I’ve got a little list
I’ve got a little list
There will none of them be missed
There will none of them be missed!
In similar vein, when my husband and I recently set off on a camping holiday to Utah and Arizona, we had a little list too (of things to bring). Alas we forgot some important items like a picnic tablecloth, towels, and Steven Austin’s book Grand Canyon: Monument to Catastrophe. This was our first visit to that part of the world and some interpretive material and tourist information on the area would have been very helpful.
Our first stop was Bryce Canyon National Park in Utah. We discovered that the park is on a plateau (the Paunsaugunt Plateau) which towers 240 m above the adjacent plain. The edge of that plateau is eroded into broadly sculpted alcoves or bowl shaped amphitheatres. However it isn’t to see a scalloped plateau edge that millions of people come to this park each year. What everyone wants to see are the hoodoo hoards, rocky columns, horizontally striped red, pink and white that tower 60 m into the air from the base of the canyon at the edge of the plateau. They look like multicoloured soldiers standing rank upon rank. Originally these were a series of closely spaced gully walls within the amphitheatre. Now they have become separated into free standing units. The harder and softer rock layers of sandstone, limestone and shale in the columns produce the knobs and joints.
With plenty of unanswered questions about the origin of these strange rock shapes, we proceeded to Zion National Canyon, also in Utah. No sooner were we in the park than totally different rock types met our astonished gaze. Some of these sandstone rocks were white, others red, but they all had a prominent criss-cross layering effect that geologists call cross-bedding. Our route took us through a tunnel (it seemed to extend forever but was actually 1.8 km long). Immediately thereafter we found ourselves descending in sharp switchbacks down an incredibly steep valley. As we retraced our steps upward the next morning, we reflected on the crossbedded rocks which rose 1000-1200 m above the valley floor. Nevertheless we pressed onward.
Once in Arizona our route carried us northeast through increasingly desolate desert to Marble Canyon. It was here that we crossed the Colorado River. The canyon walls were almost vertical with the bright green water of the river almost 150 m belong the edge of the cliff. The canyon walls consisted of conspicuous layers of hard cherty Kaibab limestone with sandstone below. Next our route took us through more desert with very little vegetation of any kind. At the tiny village of Cameron, we turned west toward Grand Canyon National Park. We made one stop at a lookout to gaze down into the dark depths of the Little Colorado River Gorge (a tributary of the Colorado River). As at Marble Canyon, the sides fell straight down. The rocks were similar in appearance but the valley floor was perhaps three times deeper. There was no river below, only a couple of brightly coloured puddles. After more driving we finally arrived at the fabled Grand Canyon.
Once inside the famous National Park, the views were every bit as spectacular as everyone claims. The elevation on the southern rim is 2100 m. Apparently the same rock layers are found 400 km east in the state, but at an elevation that is 1600 m lower. At both sites the rocks lie flat, but in between there is a steeply inclined region. Some kind of force from far below in the earth raised up the land to produce a massive plateau. The Colorado River, interestingly, does not go around the plateau but rather cuts through the height of land. The Canyon is 1200 m deep and 6-30 km wide. Most of the canyon is cut through sedimentary (deposited from water) rock. However the inner gorge at the bottom (cut through hard bedrock) is about 300 m deep and typically less than one half mile wide. Rocks of various shades of white, red and magenta trace horizontal stripes in the canyon walls. The river, far below, looks like a tiny thread of turquoise. Buttes, mesas and other rock shapes crowd the valley floor. No fault or fold structure parallel to the direction of the canyon exists. One cannot help asking where these impressive layers of rock came from, what force raised them up, and why this canyon cuts through the height of land.
After several days of sightseeing, we headed northeast. We crossed back into Utah from Arizona at Navajo Monument Valley. As we approached the state border, suddenly out of the rolling plain there appeared dramatic free standing spires, buttes and mesas. Naturally we wondered about the source of these structures. According to Dr. Steven Austin, visitors often ponder what erosional processes could have produced these features since there are no permanent flowing creeks or streams in this very dry valley. Moreover, since most of these mesas have no extensive accumulations of powdered sediment at their bases (which would suggest present day erosion), many geologists suspect that these are very old forms which owe their formation to ancient energetic bodies of water.
Our final holiday hurrah was Arches National Park, located along the Colorado River considerably northeast of the national monument. Of all the places we visited, these rocks were the most photogenic. My husband used up a whole role of film there within 30 minutes. As at the national monument, strangely shaped sandstone rocks project in sharp relief above a plateau. These rocks too were almost free of the products of erosion. How did these strange formations come into existence? We proceeded home with plenty of food for thought.
Back in Alberta, we discovered from Dr. Austin’s book, that these varied geological features are all logically interpreted in terms of a catastrophic flood. The basement rocks visible in the innermost gorge of Grand Canyon, are believed to have been produced during the creation week and subsequent preflood period. On top of these igneous, sedimentary and metamorphic rocks, thousands of feet of sediment were deposited from water early in the course of the flood. The rocks exposed at Navajo Monument Valley were much the same and thus represent early flood deposits too. At Zion, we see sandstones deposited later during the flood. Similarly the sediments at Arches were deposited later still, above such rocks as are exposed at Zion. Lastly the rocks at Bryce were laid down in a large post-flood lake — but we are getting ahead of ourselves.
The prominent crossbedding in the Navajo sandstone at Zion and the Coconino sandstone in Grand Canyon has traditionally been interpreted in terms of desert dune deposition. This explanation does not fit flood geology nor does it fit the evidence. Dunes may move across a desert but they never pile up in multiple beds such as we see at Zion and in Grand Canyon. Dr. Austin however presents evidence that highly energetic water currents can produce sand waves which do pile up in cross-bedded fashion (see pp. 32-35 in his book).
The really interesting feature in the region around Grand Canyon National Park is the Kaibab plateau or upwarp. This may have resulted from tectonic adjustments late in the flood. Have you ever stretched after you have been cramped in one position? It may be that the continents moved vertically upward and down in certain areas in response to a reduced load as the flood waters retreated. Perhaps this is what caused a north-south ridge of basement rocks (Kaibab upwarp) to move upward a vertical mile (1.6 km). Dr. Austin suggests that as this uplift occurred, sheet erosion removed recently deposited and poorly consolidated layers of sediment from the top of the rising ridge of land. That would explain why certain rock layers are missing from the Grand Canyon area but present to the north in Utah. The really interesting thing about the rising land though is its other significant effect. Apparently it trapped water to the northeast of the Kaibab Plateau. This water should have run off towards the southwest. Instead it formed two lakes: one, Lake Hopi lay roughly parallel to the Kaibab upwarp and the other: Canyonlands lay to the northeast. The location of Lake Hopi would have been in what is now the drainage basin of the Little Colorado River. Leakage or piping beneath the Kaibab upwarp perhaps caused the lake to suddenly and catastrophically drain — thus breaking through the upwarp and producing the downstream canyon. This first failure lead to collapse of the arm of land between the two lakes. This resulted in erosion of Marble Canyon and the catastrophic draining of Canyonlands Lake. Highly energetic water currents carved Bryce Canyon through slumping of the lake border. The sediments in this area may have accumulated during a post flood period of perhaps several hundred years. Similarly the carving of Monument Valley and Arches National Park took place at this time of failure.
Of course we saw only a fraction of the wonders of this remarkable part of the world. We do plan to return some time. You can be sure that next time we will make a better list. We may forget the tent and the cutlery, but we won’t forget Dr. Austin’s useful book!
Subscribe to Dialogue