Airliner Chronicles: Stuck on a Plane with a Proselytizer...

And really, I felt sorry for the poor guy who was stuck sitting with me on the plane flight from St. Louis to LAX. Oh, I wasn't trying to convert the poor guy into some religion. No, he got the full-court press from me about the importance of understanding what was going on 35,000 feet below us on the ground. He was being proselytized into the world of geology.

People who fly a lot for whatever region may be forgiven for not paying attention to the grand panorama unfolding below them, but to a geologist, the extra dimension is pure gold. Seeing a large swath of the Earth's surface grants a whole new perspective to understanding geological processes.

I didn't have a working GPS on the flight, so I had to guess our location for the first two hours of the flight, somewhere over Missouri, Oklahoma, or Texas. But it was unmistakable that we were over oil and gas country. The drilling rigs and their connecting roads could not be missed. Some politicians once described the "footprint" of oil and gas drilling on a landscape as just a few acres being torn up. Seeing the scene from above suggests that the footprint is "small" in the sense that a spider web is a few strings of dragline silk.

I was lost until the mesas and plateaus appeared. I knew at that point that we were in New Mexico, and I correctly figured out that we passed Sante Fe and Las Vegas, New Mexico. My seatmate, a Pittsburgh resident, got a bit confused about the Las Vegas part; "We're in Nevada already?". I crushed his hopes (that is NOT the way to proselytize, by the way).

The landscape turned into a rainbow of color, and I suddenly knew our precise location better than a GPS unit. We had reached the Painted Desert area of Petrified Forest National Park in Arizona. A plateau covered by basalt flows was breached by erosion, exposing the brightly colored layers of the Triassic Chinle Formation. The Triassic rocks reveal the beginnings of the dinosaur domination of our planet, and the floodplain and river deposits contain some of the earliest dinosaur species known. There is the wood, of course, and a stunning variety of amphibians and reptiles, including Phytosaurs, huge crocodile-shaped creatures that exceeded 30 feet in length.

Just west of Petrified Forest, I got the finest treat of the day, a perfect view of Meteor Crater. I put the best of the pictures up in yesterday's post.

A short time later, more colorful rocks came into view, but they were older than the Chinle of Petrified Forest. We had reached the Pennsylvanian and Permian rocks of the Supai Group. These rocks are the same ones exposed in the walls of the Grand Canyon, about eighty miles to the north. This is the edge of the Colorado Plateau, where the high flat landscape gives way to the deep fault valleys of the Basin and Range Province. Because the valleys are so deep, erosion eats away at the edge of the plateau, forming scenic deep gorges like Oak Creek Canyon, north of Sedona.

I was distracted by some wildfires burning in the thick forests of the plateau. I finally realized I was missing one of the more extraordinary features of the Colorado Plateau, the San Francisco Peaks Volcanic Field. The field is a vast basalt lava plain populated by hundreds of cinder cones, and an immense stratovolcano that reaches more than 12,000 feet in elevation, the highest point in all of Arizona. The edifice of the San Francisco Peaks has been altered somewhat by erosion; it was once 4,000 feet higher. It would have been the highest point in the lower 48 states.

The existence of the volcanic field is somewhat of an enigma. There's no obvious reason for it being here. There are suggestions that it is the result of an incipient hot spot, but the idea is not wholly accepted. The field is active; an eruption took place less than a thousand years ago.

Somewhere near the end of the flight, my poor beleaguered seatmate asked a geological question. He was wondering why there was a gigantic hole in the ground that wasn't a meteor impact crater. It was an open pit mine, probably for copper. I almost had a convert to the ages of rock!

Into the Great Unknown: Whodunnit? A Mountain Range Goes Missing

The new day, our second on the grand river, began with a startling sunrise. Sunrises and sunsets in the Grand Canyon are not like other places. One never sees the sun rise above or dip below the horizon, because in the deep canyons, there is no such thing as a horizon. Like Plato's cave, we can only comprehend the sun rising over the Earth's horizon by imagining it from the reflections coming off the adjacent cliffs. If the sun hits camp at sunrise or sunset, someone has made a big miscalculation in choosing a campsite. Staying out of the sun for as long as possible is a continuing strategy during a summer rafting trip on the Colorado.

There was a foreshadowing of today's mystery in the previous post. On our continuing journey into the Great Unknown, rafting the Colorado River through the Grand Canyon, we had passed through three geological formations, the Kaibab, the Toroweap, and Coconino. The first two formed in a coastal environment, while the Coconino developed in a sand dune dominated desert. But we ended our first day on the river in the midst of the Hermit Formation, a striking red-brown layer composed of siltstone and mudstone. The bright red color in such rocks (and the presence of sedimentary structures like ripplemarks) is strongly indicative of deposition in a river floodplain environment.

As we drew deeper into the canyon, we encountered successively older rocks, and they revealed more and more redbeds. Now there were ledges and cliffs of sandstone and other coarser sediments, indicative of a higher energy environment, such as the river channels of large floodplains and desert sand dunes. Clearly a major geologic event had taken place, one that produced a vast volume of sediments over a wide region. For a region of the Earth's crust that had remained remarkably stable for nearly a billion years, this event stood out.

We had entered the Supai Gorge, named for the four formations of the Pennsylvanian-Permian aged Supai Group. Their names are tongue-twisters: the Watahomigi, Manakacha, and Wescogame formations and the Esplanade Sandstone. Where did all these sediments come from, and how do we know? The sediments had to come from a mountain range, but any such mountain ranges no longer exist, having been eroded to rubble many millions of years ago.

Ripplemarks and crossbedding in the sediments show that the rivers were flowing in a general southwest (today's southwest, anyway) direction, meaning the mountains lay to the east or northeast. In southwest Colorado, there are younger rocks, similar to the Mesozoic rocks found around Zion and Capitol Reef in southern Utah. But beneath them where the Paleozoic rocks should be found, there are only ancient Proterozoic metamorphic rocks and intruded granites. These ancient rocks are the roots of the Uncompahgre Uplift, otherwise known as the Ancestral Rocky Mountains.

The origin of the Ancestral Rockies remains somewhat of an enigma to geologists. They coincide in time with the collision of South America and Africa with the southeastern part of North America, an event that ultimately produced the supercontinent Pangea. But the Ancestral Rockies are hundreds of miles removed from the collision zone, so geologists infer a sort of chain reaction in the crust along ancient fault systems. In any case, the rise and destruction of a mountain range in Pennsylvanian and Permian time has provided us today with one of the most scenic and colorful layers in the Grand Canyon.

I came to love two bird species who make their home in the canyon. One of them was the blue heron. We would see them all through the canyon, gracefully soaring over the water, or stepping carefully in the shallows, looking for fish and other prey.

We continued to descend deeper into the canyon. Today's route would take us through a part of the canyon called the "Roaring Twenties", a series of rapids spaced on average only a half mile apart. After the relative paucity of rapids on the previous day, it was a real roller coaster. Remembering the scale of 1 to 10 for rapids in the Grand Canyon, we faced House Rock Rapid (7), North Canyon Rapid (5), Twentyone Mile Rapid (5), Twentythree Mile Rapid (4), Twentythree and One-Half Rapid (4), Georgie Rapid (6), Twentyfour and One-Half Rapid (6), Twentyfive Mile Rapid (6), Cave Springs Rapid (5), Tiger Wash Rapid (5), and Twentynine Mile Rapid (2).

All the boats made it through the rapids without incident, until (I think) Tiger Wash. As we slipped over the tongue of the rapid, I thought I saw one of the boats go vertical, and someone tumbled out. I thought it was my nephew at first, but soon found that it was the boat with my brother and his wife. Somehow they had stayed in the boat, but unbeknownst to them, their oarsman was missing. They heard him say something along the lines of "your oarsman is NOT in the boat". They looked behind in surprise as he clawed his way back onto the raft just in time to get hung up on a boulder. Our raft was closest, so Pete rowed back into the eddy, and we started to climb up the rocks to see if we could assist, but they managed to back off the rock, and we were able to continue on.

Looking up the canyon, we could see that the monsoon storms were not finished. The towering cumulus clouds were wreaking havoc upstream, but the day remained sunny and clear for us. Tonight I would be sleeping under the stars.

We passed another stunning example of mass wasting just before hitting the Roaring Twenties. Boulder Narrows is a huge single chunk of Esplanade Sandstone that practically dams the river (below). According to the river guide, it is the single largest boulder to be found in the river through the Grand Canyon.

The canyon became deeper and more vertical.

At lunch, I was able to concentrate on smaller things, like the wonderfully colored and patterned river boulders.

The Supai Group is one of the thickest units in the Grand Canyon sequence at more than a thousand feet, so it was with us for quite a few miles. I had not been this close to the redbeds in a long time, and the ledges and cliffs made for a scenic stretch along the river. The combination of scenery, geology and rapids made for a memorable day.

There was an otherworldly appearance to the cliffs that rose above us, straight out of the river.

At mile 23, a new layer appeared, hard ledges of gray limestone. We had reached the Mississippian-aged Redwall Limestone. There wasn't a bit of red in it, at first, but that would change before long. I'll save the detailed description for the next post, because today's exposures were just a preliminary tease.

The Redwall Limestone is a true cliff-forming rock, and in places the rock hung over the river.

After the excitement of eleven major rapids and a near miss in the flip department, Pete was a bit tired. We were past the rapids of the Roaring Twenties, so I took to the oars for a couple of miles. I'm not saying I'm a natural oarsman, but the several miles I rowed probably amounted to about a half mile of actual river. I had a devil of a time sticking with the current and staying out of the eddies. Plus, you can see I didn't put on my gloves, so I also got a blister (whine, whine). It was fun!

In the next post: the incredible Redwall Limestone of Marble Canyon.

Time Beyond Imagining - A Brief History of the Colorado Plateau, Part 6: Seeing Red (Really!)

Parts of the Grand Canyon are really red. Extremely red. So red, that a hike through the red layers leaves stains on socks that will never, never come out. So red that it spills over and turns the surface of the underlying rocks red too (see the last post about this). Red enough that the river that carries this sediment to the sea (or at least used to), the Colorado, means Red River.

There are several red formations in the Grand Canyon, but the subject of today's post is a group of layers that are collectively known as the Supai Group and Hermit Formation. A group is a collection of formations that share some characteristic, such as similar rocks, age or depositional environment. There are four formations that make up the Supai Group, and they are a bunch of tongue-twisters: the Watahomigi, the Manakacha, the Wescogame, and the Esplanade. They are red. Did I mention that?

All five formations are visible in the first photo. The lower prominent cliff is the Redwall Limestone, which takes the color by staining from the overlying Supai Group (it is actually gray). The Supai Group formations and the Hermit Formation are a series of alternating ledges and cliffs that are bright red, leading to another prominent cliff, the white Coconino Sandstone near the rim of the canyon. The individual formations are not easily distinguished. The easily eroded Hermit Formation is best seen in the second picture, where it is exposed just below the white cliff of Nankoweap Butte (as seen from Pt. Imperial on the North Rim). Collectively, these layers are the thickest of those seen from the rim of the canyon, totaling something like 1,000 feet. The first three formations date from the Pennsylvanian Period (just over 300 million years ago), and the Esplanade Sandstone and the Hermit Formation are early Permian (just less than 300 million years ago).

What does the red mean? It means iron oxides, which form in the presence...of oxygen. Very few of the layers discussed so far in this series formed above sea level. The red beds formed in floodplains, river channels, delta deposits, and sand dunes, all above sea level. They are terrestrial deposits. So the Supai Group and the Hermit Formation cover thousands of square miles in northern Arizona to a depth of more than a thousand feet, which leaves us with a huge question...where did all this sand and mud come from? And why are Pennsylvanian and Permian deposits on other parts of the Colorado Plateau very different from those in the Grand Canyon?

More in the next post!