Where are the Ten Most Incredible Places You've Ever Stood? My Number 9: Frame Arch and the Delicate Arch Trail

It's the journey through the Ten Most Incredible Places I've Ever Stood! As I explained in the last post, the list is subjective, and everyone's list will be different. I'm pleased at the response of many of you already listing your most incredible spots in the comments, and on my accounts at Facebook and Google+. I'm looking forward to seeing more! My own list is not in any particular order, other than my choice for number one. Folks will perhaps not be surprised to see that I selected the picture above for my number 9; it's the cover photo from my Geotripper Images website where I've posted a lot of my geological pictures for use in educational/academic projects. It is a view of the La Sal Mountains through Frame Arch at the end of the Delicate Arch trail in Arches National Park.

In the years before PowerPoint, I started all of my geology classes with a set of slides (this was an ancient technology that involved "carousel trays", "slide projectors", and "film") to introduce the students to the world as it is revealed by geological processes. The first picture was always this stretch of trail just short of  Delicate Arch. I chose it because it symbolized so much about the wonders revealed in the incredible history of our planet.

The trail is cut into a formation called the Entrada Sandstone, a layer composed mostly of  windblown sandstone as well is silt and mud in some areas. It once was a system of sand dunes near a coastal delta and estuary during the Jurassic Period around 140-180 million years ago. The trail surface is a natural separation along the surface on one of the dunes, so by walking on this trail we are striding on the same surface that dinosaurs, ancient mammals, and arthropods walked on many millions of years ago. We know that these rocks were buried deeply by thousands of feet of overlying rock, but they were pushed upwards by vast salt domes rising from older formations below. The doming effect split the rocks into linear fins, and the arches developed from weathering and erosion at the base of fins.

At one viewpoint an observer can appreciate the variety of depositional environments that led to the formation of the colorful Entrada rocks, the vast amount of time that the rocks lay buried in the crust, the immensity of earth movements that brought the rocks back to the surface, and the intensity of erosional processes that shaped the rocks into what they are today. And one can walk on a surface that may very well have been a trackway for a dinosaur many eons ago.

But (like they say in late-night television ads), there's more! Although many people use Frame Arch to frame Delicate Arch, I chose to emphasize the La Sal Mountains instead (the top photo). The La Sals represent the role of magmas in earth processes. The mountains are composed of intrusive rock that reached close to the Earth's surface about 25 to 28 million years ago. Some may even have erupted out in volcanic eruptions, but the rest of the rock formed into mushroom shaped plutons called laccoliths. The dioritic rock proved more resistant to erosion than the surrounding shale and sandstone, so the peaks rise 6,000 to 7,000 feet above the plateau surface. The highest peaks in the La Sals reach nearly 13,000 feet above sea level.

It's a scenic, even iconic spot for photographers and park visitors, but what makes this one spot special to me? It's the unique experience of each visit. It's been my privilege to visit this spot perhaps a dozen times in the last 30 years and every time it has been an awe-inspiring journey. We usually head up the 1.5 mile trail in the late afternoon in order to catch the sunset on Delicate Arch. Quite often there is a raucous crowd, and some moron always feels a need to go stand under the arch for an inordinate period of time, prompting shouted complaints from the large group of photographers on the ridge top. Frame Arch becomes the special spot at that point because there is only myself and a few of my fellow travelers. We don't hear the chaos and mayhem at Delicate Arch, and we can just sit and appreciate the changing colors and deepening shadows.

Once or twice we've been doused with a summer rainstorm, and in one particular year we took shelter under the arch and gloried in the lightning and crashing thunder, and watched as the dry sandstone transformed into a series of waterfalls and white cascades. It was one of the most cherished moments of my life. We assumed that the storm would obscure the sunset, but as quickly as the storm hit, it dispersed and the sunshine broke through to highlight the La Sal Mountains in the far distance.

One more reason that this spot is on my incredible list is because of the ephemeral nature of Delicate Arch itself. It may not last my lifetime. The arch is only a foot and a half thick at one point, and there are valid fears that it could collapse in the natural order of events. Of course, humans may help it along; I've heard of at least one episode in which a man attacked the arch with an axe. Then again, it could last another thousand years. Who knows? In the meantime it is a magic place.

Once before I pass on I would like to see it in the snow.

Fire Down Below III - a Geological History of the Colorado Plateau

Another couple of perspectives of the volcanism that effected the Colorado Plateau between 20 and 30 million years ago.

A very accessible view of a classic volcanic neck can be had from Highway 163 a few miles south of the Utah-Arizona border near the town of Kayenta, Arizona. Agathla Peak (sometimes called El Capitan) is almost 1,500 feet high, and as can be seen in the photo on top is not composed solely of dark volcanic rock. Instead, much of the prominence is composed of large fragments of the surrounding sedimentary rock, shot through with dikes of darker volcanic rock that have more or less welded the pinnacle together. The surrounding rocks are shales and siltstones of the Chinle Formation.

The second photo is of Navajo Mountain, described at the end of yesterday's post. I had intended to include a photo, but to my surprise found very few of them in my archives. It strikes me that as I travel through the plateau country that the mountain looms in the background of nearly every part of our route. It comes into view soon after we leave Grand Canyon National Park out to the east. We drive south of the mountain as we approach Navajo National Monument and Cedar Mesa. It rises to the south when we drive through Escalante-Grand Staircase National Monument. And yet for all that, I hardly ever snapped a shot! But here is one from Cedar Mesa. The mountain is covered by sedimentary rock that has domed up over the volcanic rocks underneath.

Fire Down Below II - a Geological History of the Colorado Plateau

Continuing a long-running adventure, we pick up the tale of the geology of my cherished corner of the United States, the Colorado Plateau....we've come through 2 billion years of the story, and are now only 20 million years from the end!

Volcanic activity had not been a prominent part of the geology of the Colorado Plateau for hundreds of millions of years, throughout Paleozoic and Mesozoic time, except for the volcanic ash that drifted in from elsewhere and ultimately provided much of the color of the Morrison and Chinle formations. That all changed in Cenozoic time. As outlined in yesterday's post, there was a vast outpouring of lava and tephra across much of the western United States around 30 to 20 million years ago, which resulted in the formation of numerous volcanic necks, calderas and the subject of today's post, laccoliths.

There are some real oddities in the landscapes that make up the Colorado Plateau, islands of rock with alpine snowfields and deep green forests that seem more like the Rocky Mountains than part of a desert. These strange out-of-place mountains include the La Sal Mountains (top photo), the Abajo Mountains, Navajo Mountain, the Henry Mountains (center photo), the Sleeping Ute Mountains (bottom photo), and a number of others. The highest, the La Sals, top out at over 12,000 feet. They are a beautiful addition to the landscape; imagine Delicate Arch in Arches National Park (top photo) without the dramatic backdrop of the La Sal Mountains in distance.

How can such mountains develop out of an otherwise flat landscape?

They aren't volcanoes, not in the sense that we normally think of them, but they are volcanic in origin. The mountains are made of a semi-coarse-grained igneous rock that has a number of names, but diorite will do for the moment. 'Coarse-grained' usually means the rock results from slow cooling of the magma miles underground, but the rocks forming the core of these mountains are sort of a hybrid, showing a fine enough texture that they were probably a few thousand feet below the surface, rather than several miles beneath the surface. G.K. Gilbert was studying exposures of these rocks in the Henry Mountains in the 1870's and he realized that although there were complexities, the rocks tended to squeeze between sedimentary layers, and to make room, they pushed the overlying layers upward into a domelike structure, much like a blister pushes the skin upwards. He called these igneous 'blisters' laccolites, and eventually they came to be known as laccoliths.

A simple laccolith, courtesy of http://geology.utah.gov/teacher/tc/tc0108.htm

Navajo Mountain appears to be an ideal example of a simple dome-style laccolith. It certainly looks the part. The more complex mountain ranges include multiple laccoliths at different levels, sometimes branching out in several directions. They often probably constituted the plumbing systems of volcanoes that developed on a surface many thousands of feet above, but have since been eroded away.