The Abandoned Lands...A Journey Through the Colorado Plateau: A day in the canyonlands, part 4

The nice thing about blogging is that one gets to set one's own rules and deadlines. I'm easily distracted and can drift from one project to another, and then drift back. So it is with this project on the Abandoned Lands. Off and on for the last five months we have been examining our summer journey through the Colorado Plateau, and we've reached the 12th day of a 16 day trip. But what a day this was! It started with a fiery sunrise, included a hike to see the largest arch in the world, and added a tour of an Indiana Jones movie set ("that cross belongs in a museum!"), and it was barely past noon...

And now we were headed into the canyon lands, preserved as Canyonlands National Park and Dead Horse Point State Park. This province of the Colorado Plateau has been deeply incised by the Green and Colorado Rivers, enough to expose upper Paleozoic sedimentary rocks. We hadn't seen rocks that old since we left the Grand Canyon ten days earlier. The late Paleozoic rocks at Grand Canyon had been a mixture of marine and terrestrial rocks, but in Canyonlands, the bright red colors told us the rocks were almost exclusively terrestrial.

Except for one thin bit of beach sand ...a layer called the White Rim Sandstone (below). From our perch at Grandview Point, we were looking at the last advance of a seashore in Permian time, some 270 million years ago. It would be tens of millions of years before seas would once again cover the region.

This is a vast empty quarter; it's hard to imagine making any kind of living here, but people migrated into the region, and most abandoned it soon after. The Native Americans made the maybe the most successful effort, with evidence of Archaic peoples arriving thousands of years ago. The Ancestral Pueblo people occupied the region from 200 BCE, and another group, the Fremont, arrived around 800 CE. Both groups abandoned these lands before 1300. It was several hundred years before others reoccupied the land, with the arrival of the Utes, the Paiutes, and the Navajo. The Spaniards largely ignored the region, but outlaws in the late 1800s utilized the intricate canyons as hideouts.

One after another, others moved through this landscape: ranchers, uranium miners, trappers, gold miners, oil drillers. And then they moved on. In the early 1960s, riches of a different kind were recognized: the scenic nature of the canyons. In 1964, Canyonlands became a national park.

In contrast to the vast expanse of Canyonlands, Dead Horse Point is a miniscule property of just over 5,000 acres (8 square miles). But what a spot! It is perched on the edge of a 2,000 feet cliff overlooking the Colorado River and the eastern side of Canyonlands National Park.

There was an interesting spider in the picnic area, too! Anyone know what kind it is?

The shadows were finally starting to lengthen, but our day wasn't yet done. Most of the students made the 1.5 mile hike to Delicate Arch to watch the sunset. I headed up to camp for a different walk...

More next time!

Time Beyond Imagining - A Brief History of the Colorado Plateau: A Final Transgression

With today's post we reach the rim of the Grand Canyon, and the end of the Paleozoic rocks of the Colorado Plateau. But these pictures are not of the Grand Canyon, although some similarities exist. Both canyons were carved by the Colorado River, for instance. We are in southeastern Utah at Canyonlands National Park. Our vantage point is the Island in the Sky plateau that overlooks the confluence of the Green and Colorado Rivers. Unlike the Grand Canyon, the oldest rocks visible are Permian in age, and the upper canyon walls are in Mesozoic rocks (the age of the dinosaurs, basically).

Hikers in the Grand Canyon who have a geological background don't measure their progress in miles and feet the way normal people do. We note our location by the strata through which we are strolling. The base of the Supai Group means a long slog through red dirt. The base of the Redwall almost always means a tough climb is ahead. The greatest relief to geological hikers is to arrive at the top of the Coconino Sandstone, where we realize that only two more formations lie between us and a cold beer or iced tea: the Toroweap Formation and the Kaibab Formation. Both are easily visible in yesterday's post, the Toroweap as the forested slope above the sheer Coconino cliff, and the Kaibab as the ledgy cream-colored cliff forming the rim of the canyon. Like the Coconino, both formations are Permian in age, the very latest part of the Paleozoic Era.

The Toroweap Formation is rather variable in composition, ranging from dune sands, evaporites (forming in drying bodies of water), and limestone. It formed in a time of changing sea level, where the shoreline transgressed and regressed repeatedly, forming dune fields, tidal flats and sabkhas (coastal salt flats). Fossils are generally rare, given the harsh conditions in which the rocks formed.

The Kaibab Formation is more marine in origin, being composed of limestone, dolomite, and sand. In many places chert nodules can be found. The chert is a form of altered quartz that can develop long after deposition. The layer is rich with fossils: crinoids, brachiopods, sponges, bryozoans, shark teeth, nautiloids, fish, and some of the last trilobites to inhabit the earth (the Kaibab Formation on the North Rim of the Grand Canyon was the site of my first childhood fossil discoveries). Many of these species were doomed: the end of the Permian was marked by the worst mass extinction event ever recorded. Something like 95% of all the species on the planet disappeared, for reasons that have not yet been determined, although many hypotheses are proposed.

So why the pictures of Canyonlands National Park? Note the white rock layer sandwiched between thick layers of red rock. This layer is appropriately called the White Rim Sandstone (the White Rim is a very prominent terrace in Canyonlands), and being Permian in age, is related to the Coconino, Toroweap and Kaibab formations. The sea that formed the Kaibab and other late Permian marine layers transgressed from the west onto the continent. This is indicated in part by greater thicknesses to the west. On the other hand, the farther east and north that one travels, these layers become thinner. And thinner. By the time we reach Canyonlands National Park, the marine sands are only a few feet thick and then pinch out. We are looking in these photographs at the last beach of the last Paleozoic sea.

We have reached the rim of the Grand Canyon, and the end of the Paleozoic story. The reconstruction of the supercontinent Pangea was complete. World ecosystems had been devastated by extinctions almost beyond imagining. The world had changed completely, and the Mesozoic age had begun. Dramatic changes are coming! In another post, though....