Limestone is a unique character is the rock world. There are only a handful of rocks that can be dissolved in water, and limestone is by far the most common of that group (other members include salt and gypsum). Most limestones are composed of the skeletal remains of deceased marine organisms (a handful are formed by entirely inorganic processes), so their presence generally indicates that an area was home to a warm, shallow sea at some time in the past. Fossils of coral, clams, snails, and other water-loving critters are often abundant in limestone, and in some ways, a chunk of marine limestone IS one gigantic fossil!
The aforementioned critters make their shells out of calcium carbonate, which is soluble in slightly acidic water. Most water on Earth’s surface is slightly acidic (due to interactions with carbon dioxide in our atmosphere) so interesting things can happen when water and limestone interact…especially if you give them lots of time! In particular, groundwater is capable of dissolving huge voids in limestone bedrock over long periods of time, forming features such as sinkholes and caverns.
Limestone is an abundant rock in our neck of the woods, especially in the mountain ranges astride the Utah/Nevada border in the Great Basin. Throughout much of the Paleozoic Era (541 to 252 million years ago), this region was covered by a series of vast, warm, shallows seas, much like the one that now draws millions to the Bahamas every year.
A great place to see limestone in action is the area around Great Basin National Park. Tucked away in extreme east-central Nevada, Great Basin is one of my favorite national parks, far removed from the hoards that descend annually on many of the west’s more well-known attractions. You have to make an effort to get here and at first glance, the Snake Range of Great Basin NP looks pretty much like any other mountain island rising up out of the Basin & Range. Upon closer inspection, it’s actually home to a stunningly diverse array of landscapes: The 2nd highest peak in Nevada (Wheeler Peak at 13,065 feet), some of the world’s oldest trees, and arguably the darkest night skies in the Lower 48 all reside here.
But limestone is ultimately the reason a national park exists in this corner of Nevada. A small portion of the area was originally set aside as a national monument in 1922 to protect Lehman Caves, a stunning cavern eaten into the 500 million year old Pole Canyon Limestone. Only in 1986 was the monument enlarged into a National Park encompassing both the caves and the surrounding mountain landscape.
While small in size, Lehman Caves is exquisitely decorated with a wide variety of speleothems (cave formations). Stalactites, stalagmites, shields, draperies, cave bacon, cave popcorn, soda straws, and helectites surround you at every turn as you wander through the cave. Photos show details not immediately visible to the human eye in the dimly lit cave, revealing an underground world that looks more like a well manicured sci-fi movie set than a natural place sculpted by nothing more than the water, limestone, and time.
Back on the surface, no trip to Great Basin NP is complete without a hike to admire some of the oldest living things on the planet: the Great Basin Bristlecone Pines (Pinus longaeva). Curiously, even these trees have an intimate relationship with the limestone that is so common here. Most of the bristlecone pine groves throughout the Great Basin are found growing on soils derived from limestone or dolomite (a limestone relative). For some reason, the bristlecones seem to prefer this rock type, perhaps because many other species do not, thus minimizing competition. The easily accessible grove on the flanks of Wheeler Peak (pictured below) is perhaps the most notable exception. Here the trees grow not in limestone, but among hard quartzite boulders deposited by old glaciers.
About an hour east of Great Basin, slightly younger (~490 million years) limestone in the House Range forms another unique feature: Notch Peak. At just 9,658 feet, Notch Peak doesn’t measure up in altitude with many other summits in the region. It’s claim to fame is its 2,200 foot sheer northwest face, one of the tallest cliffs in North America. Where exactly it ranks on that list depends on your definition of “cliff,” but there seems to be little debate that it is the tallest limestone cliff on the North American continent. The peak is striking, especially when viewed from the west, where the full magnitude of its 4,000+ foot rise from the Tule Valley below is apparent.
We spent an enjoyable evening camping in the shadow of Notch Peak and had hoped to hike to the summit the next day via Sawtooth Canyon on the east side, but unfortunately car issues derailed that plan.
The least visited and most isolated of Utah’s five national parks, Capitol Reef hosts what is perhaps the quintessential Utah landscape. It is as if someone took small portions of the other four parks and mashed them into one; here you can find a plethora of arches and natural bridges, deep snake-like canyons, soaring Navajo and Wingate Sandstone cliffs, and even a few hoodoos thrown in for good measure.
The skinny sixty mile long park was originally established as a national monument in 1937, but became a national park in 1971. The odd shape stems from the inherent nature of the feature it protects: the Waterpocket Fold, a 100+ mile-long kink in the Earth’s crust known as a monocline. Creeks and rivers have dissected the fold over millions of years to reveal what is quite possibly the most colorful and diverse array of rock layers in Utah.
Capitol Reef is far from just about everywhere (which made the flat tire we experienced on the way that much more annoying). To the east and south lie the last major mountain range and river, respectively, to be mapped and added to the map of the lower 48 states. Not until the 1960s did a paved highway cross the Waterpocket Fold through Capitol Reef. In the northern part of the park, the Fremont River slices a narrow canyon through the Waterpocket Fold, its water creating one of the few habitable areas in the entire region. Petrogylphs attest to the importance of this year-round water source to ancient inhabitants. In 1880, Mormon settlers established the settlement of Fruita along the banks of the Fremont. The remains of this historic farming community and the abundant, lush green orchards and fields seem out of place in the otherwise stark central Utah canyonlands but add to the allure of the park.
Here are some of the sights from our quick trip to Capitol Reef this past weekend:
For the most part, the landscape at Capitol Reef is quite open, allowing vast views and superb light at sunset:
Not far from the park campground and visitor center are the remnants of an old trail leading up a sandy wash, then up a short but steep talus slope before arriving at a hidden basin containing hoodoos and other strange rock formations. Unfortunately it was just about noon and the light was about as direct and harsh as possible, but it was cool to explore an area off-the-beaten path yet still in sight of the tour buses below:
One of the great things about living in Southern Utah is the abundance of different climates within a small geographic area. When temperatures rise into the 90s and 100s in the low-elevation valleys, we can be in cool alpine meadows at 10,500′ in less than an hour. When snow, slush, and mud cover the trails in winter, vast portions of the Mojave and Great Basin Deserts are within a day’s drive. One of these desert areas is Valley of Fire State Park in southern Nevada, not far from I-15 between St. George and Las Vegas.
Perhaps not surprisingly, upon arrival at Valley of Fire one is greeted with an array of whimsically sculpted red rock formations. Now red rocks are hardly unique in this part of the country, and the crimson cliffs here are no more notable than those found anywhere else in Utah or Arizona. But head into the interior of the park and you soon realize the allure of the Valley of Fire. After cresting the red cliffs, the hues begin to multiply exponentially and before long you are surrounded by just about every color of sandstone imaginable.
To put it bluntly, the colors at Valley of Fire are simply ridiculous…and attributable to its unique geologic location. The rocks here are mostly equivalent to those found throughout southwestern Utah and the Colorado Plateau. The Aztec Sandstone, the dominant rock unit exposed in the park, is the equivalent of the Navajo Sandstone that makes up the cliffs of Zion National Park. Geologists just assign it a different name when it appears in Nevada and the Great Basin. Perhaps the distinct name is appropriate though, given that the sandstone seems to take on a life of its own here.
Valley of Fire State Park lies within the Basin and Range province, a vast region covering Nevada and portions of half a dozen other western states where the Earth’s crust is being slowly but violently stretched apart. As the writer John McPhee once noted, so much stretching has occurred here that 20 million years ago, Salt Lake City and Reno would have been more than 60 miles closer together. Faults are abundant in this land, and fluids associated with some of these faults have at various times leached iron compounds from the originally all-red sandstone, causing some layers to become bright white, and re-deposited them in other layers, leading to the wide variety of colors.
Some of the most impressive colors are found just to the west of the “Fire Wave” feature near the northern terminus of the park’s scenic drive:
While there are numerous hiking trails, there is also lots of off-trail terrain to explore. Some of the most spectacular scenery can be found by parking at one of the numerous pull offs and just wandering out into the rock wonderland. One particular geologic feature of note is what are known as “shear-enhanced compaction bands,” thin brittle fins of rock that rise almost vertically out of the ground and often run continuously for dozens to hundreds of yards. At first glance, these features look like mineral veins, but upon closer examination they are composed of the same material as the surrounding sandstone, but are obviously slightly harder than the host rock. In many places there are two perpendicular sets of the bands, forming a checkerboard like pattern superimposed on the sandstone.
The bands are the result not of stretching, but of compressional forces that predate the formation of the Basin and Range. Stresses associated with an earlier mountain building episode (known as the Sevier orogeny) created these funky bands by essentially “squeezing” together (and even breaking) the sand grains that make up the rock, eliminating much of the empty space between the grains and forming a miniature layer of tougher, harder, and more compact sandstone that is slightly more resistant to weathering and erosion. As a result, the bands tend to just out from the surrounding slickrock by several inches, and even several feet in some locations. For such a seemingly obscure feature, many papers have been written about these compaction bands (and similar ones in a few other locations in the region). However my understanding of the structural processes behind their formation is limited and the most recent articles about them appear to be behind a paywall. If anyone reading this has more insight into these things, I would love to hear from you.
As mentioned before, these bands are quite thin, in most less than a centimeter thick and thus, sadly, quite brittle. They are easily broken by an errant boot step so if you find yourself among them, tread carefully so that future visitors will be able to experience this unique and colorful landscape.