Exploring the Depths of the Grand Canyon...By Car?

The Grand Canyon is one of the great spectacles of the Earth. Millions of people every year stand on the edge of the abyss and peer in, taking in the vivid colors and hidden depths. Tens of thousands venture down some of the few trails that reach into the incredible gorge, and several thousand raft the river. But how many drive the canyon? Did you even know you could?

And no, I'm not talking about visiting the canyon "Thelma and Louise" style...

For more than two hundred river miles, no road crosses the Grand Canyon (plus another hundred miles to Lake Mead). Navajo Bridge near Lee's Ferry is at one end, and Pat Tilman Bridge near Lake Mead is at the other. In between in the depths of Grand Canyon there is a single road that reaches the river. It's called Diamond Creek Road, and it starts on Hualapai Nation lands at Peach Springs. It's a marvelous adventure.

Without even considering the philosophical objections to building roads through the wilderness world of the Grand Canyon (objections I completely agree with), there are staggering engineering barriers. There are a series of formations, including the Redwall Limestone and the Coconino Sandstone that form sheer cliffs. The locations of trails in the Grand Canyon are controlled almost entirely by the few locations where they can surmount the cliffs of these two layers.

At Diamond Creek, the Hurricane Fault has offset the formations in just such a way that the cliffs can be avoided entirely. For the entire twenty mile length of the road, there is nary a cliff to worry about, as the road follows the bottoms of desert arroyos and washes. The biggest worry is flash floods and mudflows, which can easily shut down the road in July and August during the monsoons (and badly inconvenience river rafters who plan to take out at Diamond Creek).

One can certainly discuss the idea that it's "cheating" to drive to the bottom of the canyon, and there is a certain validity that scenery that hasn't been "earned" by completing a stiff hike might end up being less appreciated. But many people can't handle the very strenuous hiking and many simply don't have the time. Driving down into the canyon is a unique opportunity to study the oldest rocks of the canyon, the ones that are the very hardest to access in any other situation.

Diamond Creek cuts through to the Granite Gorge Metamorphic Suite, which is the oldest group of rocks found in the American Southwest, dating to as early as 1.8 billion years ago. At roadside there are marvelous exposures of schist, gneiss, and pegmatite granite with bright shiny crystals of muscovite mica and quartz.

A bit farther up the canyon one can see the layers of the Tonto Group, a series of three formations called the Tapeats Sandstone, the Bright Angel Shale, and the Muav Limestone. The three layers formed as the Pacific Ocean transgressed and covered much of the western North American continent in Cambrian time, just over 500 million years ago. The Tapeats Sandstone sits atop the rocks of the Granite Gorge Metamorphic Suite.

That last sentence needs a bit more explanation. The boundary between the Tapeats and the Granite Gorge rocks is a profound unconformity representing a gap of more than a billion years. This unconformity is actually called the "Great Unconformity", and is an erosional surface that was witness to not one, but two major mountain-building events. The metamorphic rocks were once the core of a vast mountain range that formed 1.7 billion years ago when the North American continent collided with a set of two exotic terranes, the Yavapai block and the Mazatzal block. Imagine an island the size of California or New Zealand grinding into the edge of a continent along a subduction zone and you will get the picture. This massive mountain range eroded to a flat low-relief surface over the next few hundred million years.

Later on, about a billion years ago, the continent stretched and broke apart, forming a series of fault-block mountain ranges that reached heights similar to the mountains in and around Death Valley National Park today. The rocks of these mountains are exposed in the easternmost part of the Grand Canyon, but they too were eventually eroded down to a low-relief surface as well, although small  ridges a few hundred feet high persisted. Along the lower reaches of Diamond Creek Road, you can lay your hand on a boundary between two rock sequences with a gap of more than a billion years between them. The unconformity can be seen in the photo above where a conglomerate rests on contorted metamorphic rocks in the bit of shadowed ledge. The "Diamond" of Diamond Creek is the uniquely shaped peak on the left side of the photograph. It is actually a sliver of rock caught between two branches of the Hurricane fault system.

Another layer that is prominently exposed along Diamond Creek Road is Devonian-aged Temple Butte Limestone. Most park visitors never see it because in the eastern section of Grand Canyon National Park the Temple Butte is a discontinuous thin layer that is pretty well invisible from the rim. In western Grand Canyon it is more than 700 feet thick. It formed as a tidal estuary and tidal flats along the edge of the continent about 385 million years ago.

The most "mysterious" aspect of Diamond Creek and Peach Springs Canyon is that the tributary canyons to this creek are older than the Grand Canyon itself. It's an odd problem. Along the upper reaches of Peach Springs Canyon, there are a series of Paleocene to Miocene-aged rocks clinging to the canyon walls. They once filled the canyon, meaning the canyon was carved prior to sixty million years ago, and the rivers that carved it flowed northeast, opposite of the Colorado River today. Apparently the land subsided so that the canyons were filled with sediment, and then they were exhumed when the modern Grand Canyon was carved, most likely within the last four or five million years.

Photo by Mrs. Geotripper

Diamond Creek is a fascinating excursion. It is entirely on Hualapai lands, and they charge a fee of around $25 per person for permission to drive the road. I never mind paying the fee, because the tribe doesn't have many sources of income or all that many jobs on the reservation. The town of Peach Springs where the road starts has a very nice motel and restaurant (and not much else), and if you are a train lover, you'll be able to listen to them all night long. The rails are amongst the busiest you'll ever see.The town is on one of the last remaining stretches of the original Route 66.

Out in America's Never Never: Exploring the Grand Canyon...in Las Vegas?

Photo by Mrs. Geotripper

I'm sure no one needs to be told that visiting Las Vegas is a surreal experience. I can't even begin to imagine the army of psychologists who through the years have advised casino owners on the best ways to separate tourists from their money. I've been appalled at the... well, I can't come up with any term better than excess. Las Vegas serves as a fine definition of the word.

I wonder what the point is of seeing the canals of Venice, a circus, New York, and the Egyptian pyramids when one could presumably see the real thing? One of my stranger experiences was the time I left the South Rim of Grand Canyon and arrived at a casino decorated as...the Grand Canyon. Complete with animatronic deer and raccoons. And plastic pine trees.

And yet, strangely enough, one can explore the Grand Canyon in Las Vegas, at least in one sense, and more easily than one can in the National Park. Our journey through the American Never Never took us from the Mojave National Preserve to Sin City because of the access it provides to the Proterozoic and Early Paleozoic rocks that in the park are only found deep in the canyon at the end of a hugely strenuous hike.

Photo by Mrs. Geotripper

Frenchman Mountain rises east of the city, at the boundary between the city limits and the Lake Mead National Recreation Area. The mountain mostly falls under the jurisdiction of the Bureau of Land Management, which for decades let the land languish as a shooting gallery and trash dump. Geologists have known for years (especially since the 1960s publication of John Shelton's Geology Illustrated) that the rocks exposed on the flanks of the mountain were the same as the formations found in the deepest part of the Grand Canyon. One can easily lay one's hand across 1.2 billion years of geologic history at the exposure of the Great Unconformity (it's at my feet in the picture above, sloping up to the right). One can see the cross-bedded sandstones of the Cambrian Tapeats Formation, the remains of a shallow sea that transgressed across the western margin of the North American continent. And in the small canyon above these exposures, one can pick out trails, burrows and the discarded carapaces of some of the earliest complex life forms to be found on our planet, from the Bright Angel Shale.

It is an interesting story just explaining how rocks of the Grand Canyon came to be exposed here in the Las Vegas Valley. In short, the rocks were transported 50 miles westward by extreme extensional faulting in Miocene time, around 23 to 6 million years ago. A major detachment fault system is presumed to underly the region (below).

Source: Stephen Rowland, UNLV

It's an important and significant geologic locality, one that would be worthy of an interpretive sign and trail. In the 1990s, students and volunteers associated with the University of Nevada, Las Vegas put in a tremendous amount of work to construct such a site. It was very nicely done, with a brick walkway, sturdy interpretive signs, and a short nature trail.

This was the roadside interpretive sign that explained the value of the site (source: Stephen Rowland, UNLV)

But no good deed goes unpunished. The site was in place by 2001, and within a few short years it was completely obliterated by vandals. It sickens me beyond words that such people exist who feel compelled to destroy the good works of others.

Still, it is a great place to visit and learn a bit of geology. The signs are gone, but so is most of the trash and garbage, and a walk up the hill provides a stunning view of the most unlikely city in existence. Download the information from the UNLV website at http://geoscience.unlv.edu/pub/rowland/Virtual/virtualfm.html and you won't need the signs anyway.

Next time you find yourself in the city of casinos, here is something you can do that doesn't remove money from your pocket! Check it out...it's at the end of Lake Mead Boulevard in the northeastern part of the city on the way to Lake Mead.