Journey to Utah in 2013, part 3: through the Virgin River Gorge to Zion National Park

This post is part of a series. To read the first post, click here. To see the gallery, click here.

MOUNTAINS IN FRONT OF MOUNTAINS

Valley of Fire Highway took us east and away from the dry desert scenery of the park. We headed north on Nevada SR 169, sailing along through Moapa Valley, a slightly more verdant part of the Mojave Desert through which the Muddy River runs before it empties into nearby Lake Mead. Though we weren't in Utah yet, we had already entered Mormon country. While passing through the centers of towns dotted with LDS church steeples and small farms peaceful in the morning sunlight, I felt a deep tranquility overtake me. It was clear that I was far from the progressive town I call home. I have never been here before, and I have no idea what this place is like, I said to myself, savoring those delicious words.

To the north I could see the Mormon Mountains and behind them, the Pine Valley Mountains, growing ever larger as we approached I-15. Upon reaching the interstate we pointed our RV northeast, towards St. George, and more mountain ranges appeared: the Beaver Dam Mountains up ahead, the Virgin Mountains to our right. As we left the Mojave Desert portion of the Great Basin behind, we drew ever nearer to the geological region known as the Colorado Plateau. Underneath my lazy tranquility I felt a flicker of excitement about all the intricate landscapes I was going to see there through various lenses.

The Colorado Plateau covers 130,000 square miles, contains parts of four states, and is dense with national parks, like the ones we'd be visiting in the next week or so. The chunk of continental crust it occupies is at least 500 million years old, and it's covered with miles-thick sedimentary rock accumulated over vast stretches of time. It's not really one solid plateau, but rather a basin containing many smaller plateaus. Rivers that traverse the province, along with their numerous tributaries, form thousands of miles of elaborate canyon systems, including the Grand Canyon. Though we wouldn't be visiting that particular ravine on this trip, all the places we planned to see would be related to the Grand Canyon in a geological sense. But I'm getting ahead of the story. We still hadn't passed through the line of mountain ranges that separated us from the Colorado Plateau.

HERE COMES A GORGE

Still heading northeast on I-15, we drove by the town of Mesquite with its abandoned Oasis casino, then crossed the state line from Nevada into Arizona. Suddenly the road became a winding, tilting drive through a canyon with steep walls that exposed complex layers of rock. We had reached the Virgin River Gorge, the gap furrowed by the Virgin River as it cuts between the Virgin Mountains and the Beaver Dam Mountains. One of the most beautiful stretches of highway I've ever seen, it required careful attention on the part of our driver, who happened to be Bev just then. Had we been making this trip in inclement weather, it would've been a nerve-wracking experience, but today the sun shone on us and the clouds rested on the horizon at a safe distance from our vehicle.

Before this road was built, travelers bypassed the entire gorge, using US Highway 91. The route through the gorge was selected later as a less steep alternative for trucks, taking advantage of the path the river had cut over millions of years as it followed the dictates of gravity. This small segment of interstate took seventeen years to construct, and involved twelve different redirections of the Virgin River. It was one of the most expensive road construction projects ever completed: over a million dollars per mile, Bev told me, as she steered us around the narrow curves. 

There were pullouts for hikers and rock climbers to use. I longed to stop at one of these to explore, but we did not; we hoped to reach Zion before dinnertime. I had to be content with viewing the walls that loomed hundreds of feet above me from my vantage point in the RV's passenger seat. Our path crossed over the Virgin River several times, and I wondered if the river's sculpting action had also been responsible for the angle of the layers of rock I saw above me. Or was there something else at work here? Why were these high rock walls slanting?

CROSSING A FAULT, ENTERING THE COLORADO PLATEAU

Later I learned that the true boundary of the Colorado Plateau is the Grand Wash Fault, which runs right through the middle of this gorge, intersecting with the highway. Movement along this fault line involved the sinking of the Virgin and Beaver Dam mountain ranges, both part of the Basin and Range province, leaving the land on the Colorado Plateau side higher in comparison. When these mountains dropped down, the layers of rock on the west side of the Grand Wash Fault tilted. That's why the gorge's walls rest at crazy angles to one another.

As you can see from the photos above, there are many, many layers of rock exposed here. They are mostly the same geological sequence as what you'd find in the Grand Canyon, fifty miles away. The Lower Gorge, the narrowest portion of the canyon and the first section we encountered, displays numerous Paleozoic limestones, some as old as the Ordovician Period nearly 500 million years ago. These gray limestones form the steepest cliffs on this stretch of road.

At the Middle Gorge, the Supai Group of deposits comes into view, sloping but with fewer extreme angles, composed of rock that's predominantly red. The Supai Group is the same gorgeous red layer cake of rocks that's so prominently seen in the Grand Canyon, and its origins date back to the end of the Paleozoic era, starting from about 325 million years ago. The final section of the gorge, seen just before we reached the Utah border, showed us more of the Supai Group, with the Kaibab Formation (limestones from starting 300 million years ago) above it, and the Moenkopi Formation (red sandstone from 240 million years ago) on the very top.

At last we were among some of the rocks we'd come to visit. These formations can be seen all over the Colorado Plateau. They would be with us for the next week, and it was helpful to encounter them for the first time in the stunning Virgin River Gorge. We emerged from the gorge and entered St. George, Utah, where we stopped for gas. St. George has within its city limits all the formations listed above, plus more that we would see in the parks later: the Chinle Formation, the Moenave Formation, the Kayenta Formation, and the Navajo Sandstone Formation. These layers each represent long episodes in the distant past when the Colorado Plateau was a shallow ocean, then a seashore, and then a giant field of sand dunes, which hardened into stone.

It was my turn to take the wheel, so I couldn't take pictures for a while. But when more pretty stuff came into view, I begged to be allowed back in the passenger seat, and Bev obliged. I captured the banded beauty of the Moenkopi Formation, which appeared to have just popped up out of the land below. From here it would only be a short drive to Zion National Park.

SUBTERRANEAN PROCESSES

What geologists find odd about the Colorado Plateau is how its essential structure stayed unbroken, while on all sides of it, massive upheaval was shaping the land: the Rocky Mountains to the east, and the Basin and Range Province to the west. Somehow, in the midst of a ring of volcanic activity and tectonic movement, the Colorado Plateau remained stable and mostly untouched by deformation. That doesn't mean the region wasn't undergoing transformation, but rather that the block of crust it occupied was not being torn, folded, and scraped by major tectonic activity. Experts still aren't sure why the region avoided the fate of its neighbors. 

In addition to being mysteriously intact, the whole block of crust seemed to be cushioned by something underneath it, something that kept lifting it above the neighboring Basin and Range province. As I mentioned before, the Basin and Range had long been lower than the Colorado Plateau because of tectonic activity that made it sink. But even the neighbor's sinking action didn't account for the Plateau's increasing buoyancy, and debate continued over the true cause of this uplift. Then came a fascinating project called USArray, which has helped geologists figure out what previously unknown forces have been causing the Colorado Plateau to continue to rise.

Begun in 2004, USArray uses high-quality mobile seismograph units to create something like a combination of a CT scan and an ultrasound of the crust and mantle of the earth. In 2011, some scientists working with USArray announced their findings: the Colorado Plateau is being eroded from below, as the asthenosphere (the viscous part of the Earth's upper mantle) oozes upwards and peels away chunks of the heavier lithosphere (the crust, plus the more rigid part of the Earth's upper mantle). Once those chunks of lithosphere are gone, the asthenosphere fills the empty space and makes the overlying crustal block more buoyant. This tremendous discovery explained much about the region. It's suspected that the same process has shaped other places on Earth, too. The Colorado Plateau just happens to be a spot where geologists can observe the process in action.

A LAND OF EROSIONAL SCULPTURE

While the Colorado Plateau has stayed intact over the past 500 million years or so, its uppermost levels have been dramatically shaped in more recent times by volcanic and erosional forces. This splendor of geomorphology is what makes this block of the Earth's crust both unbelievably beautiful to photographers and endlessly interesting to geologists. Sun, wind, lava, and water: all have left their mark on this surface. Sand dunes turned into sandstone. Oceans rose and fell. Thick deposits of material were laid down over millions of years, then excavated by liquid.

Rivers and their tributaries made sculptures in the rock, each intricate and lovely. We were traveling with one of those rivers now. The Virgin River was back in the picture again. It flowed beside us as we drove eastward on State Route 9. This stream of water, looking like nothing more than a large creek, has been responsible for vast quantities of rock carving. Not only did it scrape out the Virgin River Gorge, it was the creator of the vast valley that became Zion National Park.

To this majestic location we finally arrived and began the lengthy process of selecting the perfect campsite. As we circled around comparing spots, I found myself craning my neck to stare at the vastness of the high rock walls in greedy wonder. I spent much of the first evening at Zion sitting on the bank of the Virgin River where it passed by our campground, watching water run over rocks and thinking of nothing in particular. Contact with geological evidence of the passage of unimaginable quantities of time had stunned me into silence. I felt like I was floating down this river myself, tiny and buoyant, with no direction of my own, pushed along by larger forces. I was letting go of my humanness, and nothing could be finer. 

To see lots more photos of Zion National Park, click here.