Quantcast

Backpack trip tells geologic story of Grand Canyon

The Grand Canyon is a layer cake that tells the geological story of the last two billion years. The canyon gives visitors a rare opportunity to see the distinct layers that form the Earth. (Brad Branan/Sacramento Bee/TNS)

By BRAD BRANAN | The Sacramento Bee | Published: December 8, 2016

GRAND CANYON, Ariz. -- When I first peered into the layer cake that is the Grand Canyon several years ago, I was surprised to spot a continuous strip of green between a grayish section and a red-brown one. “How could so much shrubbery grow in the desert Southwest?” I wondered as I stood at the edge of the South Rim.

It wasn’t until I revisited the Grand Canyon in October of this year that I discovered my error. Walking in that green layer, I saw a fair amount of plant life, but it was actually a green rock called Bright Angel Shale that gave this strata its distinctive hue.

The Tonto Trail lies just above the Inner Gorge, a collection of rocks that is considered the “basement” of the Grand Canyon. Green-colored rocks called Bright Angel Shale underlie much of the trail network in the Grand Canyon. More than anything else, the Grand Canyon is a product of the Colorado River, which through water and sediment has sculpted the canyon’s walls. The Monument stands in a creek with the same name. Monument Creek is in one of the many beautiful side canyons in the Grand Canyon, the jewel of northwestern Arizona. The view from the Tonto Trail, which parallels the Colorado River in the Grand Canyon. The Tonto Trail lies just above the Inner Gorge, a collection of rocks that is considered the “basement” of the Grand Canyon. Green-colored rocks called Bright Angel Shale underlie much of the trail network in the Grand Canyon.

To really appreciate the Grand Canyon, you have to go below the rim and hike to its bottom, at the Colorado River, and explore its side canyons and plateaus. A trip below the rim provides a rare opportunity to see the geologic story of the last 2 billion years, with each layer in the canyon explaining successive environmental periods in Earth’s history. A book by author Colin Fletcher captures the idea and my trip: “The Man Who Walked Through Time.”

Hiking to the canyon’s bottom provides more than a geology lesson, though. The trip includes some of the most beautiful and dramatic landscapes in the world. But I appreciate that beauty all the more by understanding how it came together.

“The Grand Canyon is quintessential canyon country. The bones of the land here lay bare,” Michael Collier writes in “An Introduction to Grand Canyon Geology.” “Geology as cinema, moving slowly enough that we can examine time frame by frame.”

I took a four-day trip covering 30 miles on three trails -- Hermit, Tonto and Bright Angel. I started on the Hermit Trail on the park’s western edge after riding a shuttle bus from where I’d parked my car. I finished the trip at the start of the Bright Angel Trail, the most popular trail in the park, and a short distance from my car.

Descending the Hermit Trail provides a good cross-section view of the canyon with the Hermit Creek to the west and the Colorado River to the north. I could make out some of the 12 layers that, according to Collier, form the Grand Canyon. Kaibab Limestone lined the rim, the Tapeats Sandstone was several layers below and the Vishnu Schist formed the bottom.

The layers were stacked “like a plate of pancakes, with the newest ones going on top,” said Elizabeth McKay, a National Park Service naturalist at the park.

The Vishnu Schist was formed 2 billion years ago, and water later brought in successive layers. “Most of the rock layers we have is just the story of sea levels rising and falling,” McKay said. The rocks and fossils in each layer paint a picture of an environment in a particular period: Desert covered the area during the time of the Coconino Sandstone that can be found near the top of the canyon, for instance.

I smiled at the crushed green rock on most of the trails I crossed. McKay told me that millions of years ago, the seas were full of creatures called trilobites responsible for the color of Bright Angel Shale. “It’s green because of trilobite poop,” she said.

Moving my way through the rock layers, I was preoccupied with the steepness of the trail. The Grand Canyon is a mile deep, and to get from its rim to its bottom on the Hermit Trail is a 9-mile trek. Put that way, it almost sounds like a pleasant descent. Actually, it’s quite steep, especially the first 2.5-mile segment, which drops almost 2,000 vertical feet.

Hiking in the Grand Canyon is similar to hiking in the mountains, with a lot of time spent climbing and descending. Thinking about the canyon as a mountain is also a useful geological analogy. The canyon was shaped by the formation of the Colorado Plateau, which was made by the same colliding of tectonic plates that created the Rocky Mountains, and raised this part of the country 6,000 feet, McKay said.

But more than anything else, she said, the Grand Canyon was formed through erosion by the Colorado River: “The river is why we have this big, beautiful canyon.”

The river serves as a primary water source for several states, including California. A tremendous amount of sediment adds to the river’s destructive force, with the river collecting mass as it winds through the arid West, growing into a muddy beast.

I followed the Hermit Trail, shortly after joining the creek of the same name, and ended at the Colorado River. I had planned to camp on the beach. But the roar of the Colorado River as it slams through the Hermit Rapids convinced me I would not get a wink. I don’t know that I have ever heard water so loud. I have slept in tents next to the Pacific Ocean and stood next to falls in Yosemite and that noise didn’t compare to this.

I set up camp alongside the Hermit Creek instead. While at the beach, I scanned the horizons and was surprised I could not see either rim of the Grand Canyon. I had been swallowed by the canyon.

Later that day, I met a group of river runners on the beach. Most of them work for outfitters, and when the season ended, they got together to spend 23 days floating the length of the Grand Canyon for fun. They told me the Hermit Rapids were of average difficulty and the start of progressively more serious rapids. The Hermit Rapids were so loud I kept asking them to repeat themselves. One of the rafters brought a surfboard and was considering a ride on the Hermit Rapids.

Amazingly, the rapids are a shadow of what they were before the damming of Glen Canyon upstream about 50 years ago. By chance, I got to see what the Colorado River looked like before the dam, by watching a silent movie of a river expedition in 1923 shown at the Indian Gardens campground on the last night of my trip. In the clip, the free-flowing Colorado smashes boats to bits and forces arduous portages along steep canyon walls.

Several other creeks flow into the Colorado, and these waterways made the canyon up to 13 miles wide by pulling the walls farther apart through erosion, according to Collier.

The creeks helped cool me off. In the canyon’s depths, temperatures reached the lower 90s, which in the midday sun felt much hotter. It might have been a “dry heat,” as Arizonans like to joke, but it was staggering, regardless. I was anticipating each creek for miles. Monument Creek provided the added pleasure of running through a smooth rock formation. I sat in it, blissfully enjoying the cool water as I gazed at the tall spherical “Monument” sitting in the middle of the side canyon. The Monument is a rock formation that juts out of the creek’s floor and rises as high as the side canyon’s walls.

Sufficiently cooled off, I continued hiking along the Tonto Trail, which parallels the Colorado River and is mostly flat except for trips into the side canyons created by the creeks. I was walking across the Tonto Platform, a large plateau that struck me as odd given its location deep in a river canyon. The platform sits above the Inner Gorge, the wall of rock leading to the Colorado River.

By the time I reached Horn Creek I was burning up -- so hot, in fact, I sat in the water even though I knew it was radioactive from uranium mining. The Park Service says the water is “radioactive so don’t drink it unless death by thirst is the only other option,” but doesn’t say anything about sitting in it. I’ve survived at least to write about the experience.

 

For more information 

 

Grand Canyon backcountry permits: www.nps.gov/grca/planyourvisit/backcountry-permit.htm

U.S. Geologic Survey explanation of Grand Canyon geology: http://3dparks.wr.usgs.gov/coloradoplateau/grandcanyon(underscore)strat.htm

0

comments Join the conversation and share your voice!  

from around the web