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Tuesday, March 27, 2012

Rocks For Shots

How knowing a little geology makes you a better landscape photographer

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Water-sculpted Navajo Sandstone in Antelope Canyon, Navajo Nation, Arizona.

I can still recall the first time I laid eyes on the red rock country around Moab, Utah. Having spent the first 18 years of my life in the rolling green hills of New Jersey, it was like stepping out of a spaceship onto the surface of Mars. Nothing could have prepared me for this other-worldly landscape of soaring cliffs, deep canyons and sparkling snowcapped peaks. As alien as the land seemed, or perhaps just for that reason, I was compelled to learn more about how this remarkable assemblage of rocks came to be. My bookshelves soon overflowed with geology books on the region, and as my knowledge increased, I discovered that I could use this information to locate beautiful subjects to photograph, just like geologists know where to look for gold based on their knowledge of the terrain.

The Left Fork of North Creek flows over a ledge of maroon-colored Kayenta Formation in Zion National Park, Utah.
A Brief History Of The Colorado Plateau
Before I explain how I did this, allow me to provide an overview of the geologic history of this remarkable region. Known to most of us as the red rock and canyonlands country, the Colorado Plateau contains all the famous rivers, canyons, mesas and buttes of the American Southwest, from the depths of the Grand Canyon to the windswept heights of those snowcapped peaks above Moab. This major geologic province measures 130,000 square miles in extent and covers four Western states. To outline the region, trace a rough line from the Uinta Mountains in northeastern Utah down to Las Vegas, then southeast through Sedona, Ariz., to Albuquerque, N.M., and then north through western Colorado back to your starting point.

No other place on earth comes close to matching the overwhelming display of bizarre landforms exposed here. What confluence of geological events in the distant past created this remarkable landscape? To sum it up in a nutshell, this crumpled, dissected, convoluted country owes its looks today to the fact that it spent most of the last 500 million years either slightly above or slightly below sea level as a mostly featureless flat surface. As sea levels fluctuated due to periodic Ice Ages or enormous ocean-floor basalt flows, or as the land itself rose or fell due to tectonic forces, ocean water would invade across the low, flat landscape and retreat again when sea levels dropped. When the sea flooded the land, thick layers of limestone were deposited on the ocean floor, and fine-grained sediments, supplied by large rivers, rained down into the depths. When the seas retreated, these same sediment-laden rivers swept across the land surface and deposited enormous quantities of sand and mud on their extensive flood plains. When changing climate dried up the rivers, these sandy sediments would blow across the region to create vast dune fields reminiscent of today's Sahara only to be inundated again by shallow seas. This never-ending ebb and flow between wet, dry, riverine and oceanic environments eventually laid down a layer cake of river floodplain, tidal mudflat, shallow water and eolian (windblown sand dune) deposits, which have now been uplifted and exposed for us to photograph. Talk about luck!

Evening light illuminates hoodoos of Entrada Sandstone in Goblin Valley State Park, Utah.
As we look into the details, the story gets even more interesting. Remember those rolling green hills of New Jersey where I grew up? It may seem difficult to believe, but the Appalachian Mountains actually played a key role in the formation of the rock layers across the Plateau. Travel back in time 300 million years when the Appalachians were of Himalayan proportion, located near the equator and perhaps the highest and most extensive mountain range the planet has ever seen. This enormous range extended from what's now northeastern Canada down through Texas and central Mexico. The lands of today's American West were a vast floodplain to the northwest of these mountains where huge rivers transported and deposited prodigious quantities of sediments during their journey to the sea. As these sediments were laid down over the next 100 million years, the landscape varied between lush dinosaur-infested Jurassic swamps and vast sand dune fields. The largest of these dune fields produced the famous Navajo Sandstone we see today. Remarkably enough, when we look at the most familiar layers of Navajo, Kayenta, Wingate, Chinle and Moenkopi now exposed all across southern Utah, we're seeing the eroded remains of the Appalachian Mountains. At this same time, a comparatively miniscule range called the Ancestral Rockies rose in what's now Colorado and contributed its sediments to the mix as well (these mountains were worn flat by the time today's Rockies rose and have no relation to them).


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