GRAND CANYON PART I: THE GEOLOGY STORY
Location/Geography: North-central Arizona. Coconino County. Closest city or town: Flagstaff; Williams. Area: 1,217,403 acres (1,904 square miles/3,064 km²). Colorado Plateau physiographic province of the Western United States. Kaibab Plateau region that was fractured millions of years ago (hereafter, “myr”), resulting in seven major parcels: the Marble Canyon Platform east of the canyon; the North Rim's Kaibab, Kanab, Uinkaret, Shivwits plateaus; and the South Rim's Coconino and Hualapai plateaus. Coordinates: 36º06’N 112º06’W (http://bit.ly/1t60XIb)
Introduction: Consider this compact textbook what the title states and presents in a terse and comprehensive explanation. The information takes the reader beyond the scenery and explains the how-what-when-where-why (and) who aspects. Thus, a straightforward interpretation of geology, flora and fauna, and human history. Consider this text in the guise of a Grand Canyonology 101 class. In other words, an educational tour de force that covers all the essential information.
The Basics: The Grand Canyon is an ancient landscape of time and erosion. Its nearly 2-billion-year geologic history was created in a relatively short span of time (read, “in the blink of eye”). With opposing rims of varying elevations, this mile-deep chasm is like no other canyon on the planet. It even has a secret to its past. Namely, the intrigue of how these former high plateau environs were initially breached by a drainage, whose hallmark eventually led to erosion and exposure of the numerous layers beneath the sedimentary rind in this region. There’s more to the geomorphology (i.e., the study of the physical features of the Earth). However, for now, think of time and the elements of erosion as the secondary catalysts after the drainage started a sequential process for the future Grand Canyon in the making.
Given this abstract, there are two notable versions of the Grand Canyon’s process of creation. The first is the easier version based on the Colorado River drainage entering this unvarying terrain of the future named Colorado Plateau, which came from the northeast. The river then etched its pathway across the unbroken plateau and exited from the southwest. In time, that single, large plate fractured into seven gigantic parcels (as previously mentioned). Most people accept this interpretation as credible because the Colorado River flows through the canyon from the northeast to the southwest.
The second version, however, is more entailed (read “theoretical” and “mitigated”) and most people aren’t aware the Grand Canyon got its start from the southwest. To imagine such a scenario requires additional thought, whose subject matter is explained in more detail in part three, and for those who want to read the narrative.
More Essentials: Grand Canyon National Park (hereafter, “GCNP”), which is entirely within the State of Arizona, is designated both a Natural Wonder and World Heritage Site. Nearly 300 miles (482 km) long and averaging 10 miles (16 km) wide, Marble Canyon in the eastern sector was not originally included in the national park’s acreage. However, its 60-mile (96.5 km) annex was eventually added to the Grand Canyon’s domain. Located at mile-60 downstream from historic Lee’s Ferry, this locale is where the Little Colorado River merges with the Colorado River and is the only major tributary feeding into the Grand Canyon.
Before such status (of Federal Government protection) was acquired, the Grand Canyon was vulnerable to development by a variety of industries, including mining and logging. President Theodore Roosevelt first visited here in 1903, realized what was happening, and would continue to happen, and sought protection for the canyon’s environs on both rims. However, he achieved only Congressional approval for a Game Preserve status, which happened on November 28, 1906. Later, on January 1, 1908, the protection extended to national forest lands along both rims and changed the preserve status to the status of a National Monument. Although he tried for many years for the coveted protection of a National Park, on February 26, 1919, it was President Woodrow Wilson who finally made it official: Grand Canyon earned this highest distinction.
A Grand Overview: The Grand Canyon’s genesis of various foundations were laid down over two thousand million years. That said, the canyon’s sculpturing by erosion over the eons happened in far less time (i.e., in the millions of years). Consequently, a foundation of primeval materials laid down during the Precambrian Era and extended to the Mesozoic Era hundreds of millions of years later was a relatively recent event in the canyon’s continuing process of creation. The fabrication of the Grand Canyon, therefore, entails a sequence of timely processes that began long before the excavation of its original materials began.
Most of the canyon’s formation layers throughout this region also replicate the Colorado Plateau’s sedimentary materials that were laid down from the Phanerozoic Eon’s combined geologic record (i.e., denotes a timespan covering the whole of time since the beginning of the Cambrian Period, and comprising the three principal eras of the Paleozoic, Mesozoic, and Cenozoic geologic record). The oldest formations are stacked at the bottom, and, therefore, a straightforward geologic scheme of events. The remains of most of the Paleozoic Era are exposed in the Grand Canyon, even though, at one time, formations from the ensuing Mesozoic Era were also deposited. In fact, the entire Colorado Plateau was once covered by accumulations of various sedimentary rock layers (mostly, sandstone and limestone), whose average thickness may have been somewhere around 15,000 feet/4,572 m). Today, the Colorado River excavates the rock formations of the Grand Canyon some 2,400 feet (732 m) above sea level. Think how much higher its channel was before burrowing down into such great depths!
And so, over the eons, varying accumulations compacted, congealed, stacked, and then were stockpiled for millions of years. As previously alluded to, the entirety of this region amounted to an excessively large landscape for hundreds of miles in all directions and defined by a broad, intact plateau of enormous dimensions. In the greater distance, volcano profiles barely stood out; otherwise, there wasn’t a stream or a river or a forest or anything remarkable about this uniform and bland terrain that would one day define the northwest quadrant of the State of Arizona. However, when the future named Colorado Plateau Province was created, its former low-lying basin was poised for a consummate facelift, by way of a geophysical uplift of its complete foundation (caused by plate tectonics, which will be discussed further along in this text).
Recalling how sedimentary rock accumulations had steadily piled up over hundreds of millions of years, the thickness throughout the Colorado Plateau region defined the same layers that were eventually exposed by various rivers and streams. Mainly, it was two master drainages that incised their courses into the unbroken terrain. Namely, the Green and Colorado Rivers. Over millions of years, both drainages created deep chasms in their wake. Other drainages also did their part but were not as assiduous as the two siblings. Their combined etched and sinuous pathways into the sedimentary materials define much of the exquisite topography in parts of the Four Corners region.
The Awe And Artistry Of Erosion: In this quadrant of North America, erosion rules! It follows how exposed rocks are susceptible to erosion by physical and chemical agents, but mostly wind and water do the honing in this typically arid part of the Southwest. As mentioned, the Grand Canyon is an ancient landscape that was eroded over time. That process has revealed all the rock formations that were laid down and were eventually exposed and eroded. The upper layers (above the inner canyon gorge), are especially revealing, whose banded and colored profile feigns an open geologic textbook on display.
Using one’s imagination, think what this regional setting must have looked like before the layers were exposed. Monotonous, relatively flat, sterile, and vast emptiness are common adjectives most geologists would use to describe the scene long before the Colorado River (or some other drainage) flowed into this sector. Now go back the other way, say two billion years, and watch what happens when the drainage flows into this region, then carve its bearing across the featureless landscape. Continue waiting and watching as that drainage lengthens and deepens its groove. One by one, the formations are exposed, and then erosion sets in. Time, erosion, and easily penetrable malleable materials. That’s about the gist of he canyon’s creation story (minus a key factor soon to be explained). Eventually, aesthetics plays a role, for the way the Grand Canyon was honed, the physical and chemical weathering agents, as well as faulting, enhanced its features to the highest order––sublime.
Of course, there is more to the process of the Grand Canyon’s process of creation than this common explanation. For instance, the Colorado River (or some other drainage) had maintained its course by a helping hand of Nature, as it were. Thus, the previously mentioned uplift event beneath the Colorado Plateau’s foundation that abetted the river’s downcutting into the terrain. Moreover, the uplift and downcutting events were simultaneous, the same as happened wherever canyons were made throughout the Colorado Plateau. For now, and restating the theory mentioned at the outset of this text, let’s assume the Colorado River did the deed (because this theory is the easier of the two prevailing explanations why and how the Grand Canyon was created).
Layered Cake, Anyone? To grasp the significance of how canyons in this part of the Southwest are created, imagine a gigantic, thick cake, slightly dome shape, and rising while holding a knife, then steadily slicing downward. In effect, this tasty simulation entails the analogy of the Colorado Plateau’s landscape uplifting, as a forceful drainage like the Colorado slices into the sedimentary layers one formation at a time. That knife has long ago sliced through all the upper layers throughout the Colorado Plateau, and here, in the Grand Canyon, the downcutting drainage has since penetrated the hard-rock foundation of the cake. To wit, the erosional remains of an ancient mountain range known as the Vishnu.
Arguably, the Grand Canyon is the most stunningly beautiful canyon because of its singular step-canyon wall profile. Indeed, the aesthetic fabrication is so awe-inspiring, and on such a grand scale, the Grand Canyon earned the award for being one of the Seven Natural Wonders, and some say the Natural Wonder. The canyon’s appearance and its geologic revealing textbook represents a landmark that’s also nearly half as old as our planet. Surprisingly, it took that amount of time to collect all the materials, starting with metamorphic rocks, and then layer-by-layer of a variety of sedimentary formations. What’s the surprise? Just this: the Grand Canyon is indeed primeval by one standard, yet very young by another standard. That part of the story will soon be explained in finer detail.
Additional Background: Using the analogy of a clock of time for the Earth’s 4.54 billion years, the primordial materials for the future Grand Canyon are laid down, and the accumulation begins. The hands will move around the clock two complete revolutions, eventually reaching toward midnight. In a mere twenty-four hour span, the canyon’s creation happens only moments before the twelve strokes are sounded. Remember: the process that started ticking nearly two billion years ago describe what happened here during this encapsulated benchmark. Hence, the accumulation of materials, thence a catalyst that came along and breached the upper rind of the region, and soon followed by extensive erosion. Given this timely analogy, what time do humans show up? We barely made an appearance before the final strokes of midnight!
Making A Canyon “Grand” Entails A Process: What makes this chasm so grand chiefly has to do with its impressive dimensions and sui generis profile like no other canyon. The canyon’s length is measured from Lee’s Ferry, which is below Lake Powell (14 miles/22.5 km downstream from the Glen Canyon Dam.) Designated mile-0, the Colorado River at this sector flows through the Grand Canyon to its terminus, at the Grand Wash Cliffs mile 277.4 miles (446.9 km). Relate the distance to a road trip, say, Los Angeles to Las Vegas or Chicago to St. Louis. The width varies from 4 to 18 miles (6.4 to 28.9 km) and averages 10 miles (16 km). The average width defines the central corridor below Grand Canyon Village. From the bottom the canyon to the South Rim, the canyon’s depth averages 6,000 feet (1,829 m) and is one of the deepest chasms on the planet. There are three main corridor segments, which means visitors never view the entirety of the canyon from any perspective. Namely, the Upper, Middle, and Lower Granite Gorge. Consequently, the perspective from either rim is dizzying for some visitors but also breathtaking due to the rarefied air (i.e., the high elevation of both rims).
The Grand Canyon’s numbers are impressive! From the rim to the river, there is an amazing change of topography and features that affects the ecology of the inner canyon. Consider the opposing rims heavily forested landscape compared to the arid desert environs far below. Capped with the same Kaibab Formation limestone, this cliff-forming sedimentary rock preserves the integrity of the upper canyon walls. Next, consider the elevation above sea level factors: the South Rim elevation averages 7,000 feet (2,133 m) above sea level while the North Rim averages 8,000 feet (2,438 m). However, the peak elevation on the North Rim is 8,900 feet (2,703 m) in the eastern sector and significantly drops to an average of 4,000 feet lower (1,219 m) in the western sector (and goes down to 1,200 feet/365.7 meters at Lake Mead). The main contrast between the rims on either side of the Colorado River is climate, entailing a distinct change and adaptation for flora and fauna. The North Rim also receives most of the precipitation, both rain and snow, while the western sector (on both rims) receives much less. Now consider the extreme of so-called dry climate at the bottom: an overall average of some 8 inches (20.3 cm) from one end of the canyon to the other (nearly 300 miles/482 km)!
As the canyon raven (Corvus corax) wings its way from the central corridor (in the Grand Canyon Village sector), it's about a 10-mile (16 km) flight from the South to North Rim, yet hiking the Bright Angel Trail, which connects to the North Kaibab Trail on the other side of the river, is 24 miles (39 km). If driving from the South to the North Rim, it’s a whopping 225 miles (362 km)! Although there have been suggestions over recent years to build a bridge from one rim to the other, hence, a way to beat the raven’s time when crossing the canyon, the NPS essentially says “Nuts!” to this idea. Still, there is a rumor the Hualapai Indian Nation, which owns the Grand Canyon West sector, might consider such an enterprising idea. However, the question is twofold: Will they take the dare and who would put up the money for such extravagance for the sake of just that––extravagance?
Of the two sides of the canyon, the South Rim receives more visitors chiefly due to its accessibility close to the I-40 and I-17 corridors (both intersecting at Flagstaff, some 80 miles (128 km) to the south. More importantly, the South Rim is opened year-round and offers more tourist amenities (hotels, shops, and restaurants). The North Rim is, therefore, the remoter locale and is not favored by proximity to major thoroughfares or having an abundance of tourist amenities. Moreover, it’s less crowded domain is closed from around mid-October to mid-May, typically due to heavier snowfall.
Additional Background: The persistent drought throughout the Southwest since the early 1990s has reduced snow accumulation by, at least, thirty-five percent (and, in some years a greater percentage). Hence, the dates of closing tourist facilities are likely going to be around two weeks either way; that is closing the North Rim from early November to early May. Of course, the real contingency in the matter is the prevailing dry cycle affecting most of the Southwest, and whether its limited precipitation throughout the Colorado Plateau will remain just that––limited.
Geology––Two Distinct Canyon Profiles: For most people, the Grand Canyon’s famous characteristic comes down to its geologic configuration and erosional fabrication. Hence, the all-embracing appearance that, in some way, doesn’t look like a canyon. That said, and quite unlike typical V-shaped chasms such as Hells Canyon in Idaho or the Black Canyon of the Gunnison in Colorado, the Grand Canyon’s upper formations defines an unusual stepped profile. As a result of erosion and the varying types of rock layers in its foundation, it is, therefore, a uniquely fashioned and distinctive canyon profile. Furthermore, the upper walls of the canyon are stratified and distinctly banded, with the oldest formations stacked at the bottom. These congealed and compacted depositions account for two-thirds of the canyon’s formations, rising sheer above the deeper and darker gash of the inner canyon gorge (aka “metamorphic core complex suite”). Each layer also represents different marine and terrestrial environments that came and went over millions of years.
Roughly speaking, the Grand Canyon formations, as varying sedimentary rock depositions, began forming during the Cambrian Period (541 to 489.5 myr). The formations, therefore, represent distinct periods from the Paleozoic Era’s geologic record (541 to 254.2 myr). Consequently, this opened geologic textbook benchmark defines a profound life-giving sequence of sub-chapter environmental events when life forms first appeared on the planet; that is starting with single-cell primitive life that mostly spawned in shallow oceans and seas. The thick limestone layer that caps both rims also marks the end of this era. That said, at one time, there were numerous other formations stacked on top (from the ensuing Mesozoic Era). This explanation soon follows.
The materials of the Grand Canyon’s formations principally consist of the previously mentioned limestone and sandstone, but also a mix of conglomerate, breccia, and shale. These five classifications define sedimentary rocks. These depositions were laid down horizontally while below the upper canyon layers the inner canyon gorge denotes a marked vertical profile. This V-shaped sector of the canyon is where the Colorado River flows (and is visible from either rim only in select places). Known as the basement rocks, the formations are relatively harder metamorphic rocks, meaning new materials made from older sedimentary or igneous materials. For the most part, this foundational landscape reveals remnants of the primeval Vishnu Mountain Range. Thus, a lifeless time on the planet denoting the Precambrian Era. Compared to the Paleozoic Era formations laid down over millions of years, the Precambrian’s much longer time span is about 4.5 billion years and ends around 600 myr (give or take). In places, there was a secondary event of Precambrian formations deposited called the Grand Canyon Supergroup. These tilted and stratified (i.e., horizontal) layers overlie the ebony-colored schist of the remains of the Vishnu Range. Nearly half as old as the planet, the inner canyon gorge represents what geologists refer to as deep time. Indeed, walking from the rim to the river replicates a bona fide time machine, where each average step is about two-thousand years!
A Monumental Marble Cake Thousands Of Feet Thick: The earlier analogy of a layer cake is fitting because the upper walls of the Grand Canyon reveal distinctly banded layers and tinctures about each formation (i.e., the varying environments each represents). Since marble is a form of sedimentary rock (i.e., limestone), only undergoing more intense heat and pressure, such as happens to all metamorphic rocks, the Grand Canyon’s shapely contour from top to bottom is certainly distinguishing from all other canyons on the planet (bar none). Like a wedding (marble) cake, beneath these ten or so basic layers is a hard-rock pedestal. It is this much older metamorphic foundation (mostly metamorphic) that reveals an entirely different look and feel of the Grand Canyon’s setting, where one can think of the vertical layers––the darker canyon profile––holding up the horizontal (cake) layers. Hence, a Grand Canyon in all its splendor (the upper layers). That said, the vertical canyon is easily outstanding (as a feature) compared to the horizontal layers. It follows how the age factor difference between the two unique foundations is equally evident. Thus, the Precambrian Era foundation of the canyon compared to the relatively recent upper story layers that were laid down over a course of around a few hundred million years.
The pedestal portion that supports the cake layers manifestly entails two encroaching eras of the Precambrian (meaning “before life”) and Cambrian Eras. Thus, the former being essentially lifeless, and the latter a benchmark of evolutionary life forms, starting with simple marine environments. At this benchmark, Nature took Her time preparing the planet for a life-friendly atmosphere, and the ensuing variety of life forms. Originating in saline and clear-water oceans and seas, some of the life forms eventually traded their gills for lungs and came out of the water. In time, new life forms were spawned on land. Consequently, a lengthy record of interspersing marine and terrestrial environments that happened here over millions and millions of years.
However, here another interesting fact is pointed out: the difference between the two distinctive phases represents well over a billion years! In other words, the original Vishnu Mountain foundation of the future canyon in the making represents a span of time from roughly 1.8 billion to 1.2 billion-year benchmark while the second phase (the “Supergroup”) foundation represents 1.2 billion years to around 600 to 700 million years. Afterward, begins the Cambrian era’s introduction of life forms somewhere around 540 million years.
(Given some estimates by geologists, the Precambrian events might have begun around 1.7 billion years. Hence, a bit shorter lifespan, though, nonetheless, still an ancient account of the Precambrian phase.)
What these figures in billions and millions of years represent is not only staggering to the imagination but also a puzzle to geologists. In short, the jump from before life to life-forming events represents a geologic event called an unconformity. In other words, there is an obvious discontinuity between two different eras and benchmarks. Another way to think of it is to use the phrase “Great Unconformity,” which is a geologic designation Major John Wesley Powell devised when he and his men explored the inner confines of the Grand Canyon in 1869 (and were the first to do so).
Although this combined subject matter is taken up in part three of this presentation, and, therefore, presents a more detailed exposition for the reader to ponder, suffice it to say the amount of time entailed in the Great Unconformity is one of those jaw-dropping incidents when people hear the number––1.2 billion years! That’s a fantastic benchmark relative to missing time, which correlates to missing pages in the Earth’s geologic record. Accordingly, whatever geologic events happened during this period, no one knows. This telltale difference marking the Precambrian from the Cambrian eras is also evident; that is once one knows where and what to look for, the distinguishing boundary of the two eras can be seen from the rim.
Notably, where the Precambrian Era’s rock foundation comes in contact with the Cambrian Period’s rock layers, hundreds of millions of years of missing formations have been removed from Grand Canyon’s geologic book of time. It’s as simple as that. The question most people have, as do geologists, is what happened during this immensely long span of time? In other words, what happened to that geologic record that was either wiped out or perhaps didn’t exist in some places (i.e., as primal depositions)? This intriguing question may not have a reliable answer, but it is thought by most geologists how erosion wiped out all events relative between the two benchmarks. Whatever happened, the rest of this fascinating story follows further along in this series.
Fundamental Facts: Here are twenty-five relevant details about the canyon, which are the kind of facts most people are curious to know:
The Colorado River below Grand Canyon Village is 2,400 feet (731 m) above sea level. Along its 1,450 mile (2,333 km) cascade down from the Rocky Mountains (near Rocky Mountain NP) to the Gulf of California (although the river no longer gets this far due to over-tapping and dam-trapping of its resource). Once the Colorado exits its namesake (the State of Colorado, as a general bearing its sinuous course is south-southwest. Carving a series of canyons in the Southwest quadrant, the sedimentary terrain was easy to carve its deep groove. However, it’s the elevation drop measured in distance that determines the rate of excavation. For instance, the Colorado River loses some 2,000 feet (610 m) inside GCNP, creating a series of rapids (aka “whitewater”). More details about these world-class rapids follow further along.
Lee’s Ferry, the originating point for rafting through the canyon, is the only place to launch a variety of watercraft for the down-river run into the Grand Canyon. This historic site for private and commercial tour operators is some 14 miles (22.5 km) below Lake Powell's Glen Canyon Dam. At the western end of Grand Canyon lies the other large artificial oasis, Lake Mead. When its basin was full (before the onset of drought in the 1990s), Pearce Ferry (sometimes spelled “Pierce Ferry”) was the primary takeout point for Grand Canyon river runners (who in some circles are affectionally called river rats). However, since then lake levels have steadily and dramatically dropped due to extensive periods of drought, with the longest lasting being some twenty years (and holding). It follows how Pearce Ferry has been high and dry above the river's channel for many years. Fairly recently, however, a closer takeout point, Diamond Creek (mile-232), which is some 60 miles (96 km) miles upstream from Pearce’s Ferry) and appeals to most commercial rafting companies, as well as private rafting parties. Located on the Hualapai (pronounced “wal-la-pie”) Indian Reservation, which is about 22 miles (35 km) down-canyon from Peach Springs, this sector of the Grand Canyon West domain can still be rafted as a day trip (or overnight two-day excursion), and mostly operated by commercial river runners. However, it requires extra time motoring downstream on Lake Mead to the nearest takeout point near Meadview AZ (South Cove). There is also the option of taking a shorter, and more popular, excursion below the Grand Canyon Skywalk, whose takeout point is about 40 miles (64 km) downstream from Diamond Creek. Exiting the canyon also requires taking a helicopter to the rim. Be advised this rafting-helicopter excursion is solely managed by the Hualapai Tribe. Hence, booking the Grand Canyon West one-day excursion is arranged by the tribe.
Take Heed: Sometimes the weather is not cooperative, necessitating rafters continue downstream to South Cove, which makes for a very long scenic day on the river and lake.
The average South Rim trail distance from rim-to-river is about 10 miles (16 km) and marks the central corridor. The shortest trail is the South Kaibab (near Grand Canyon Village) to the Colorado River––7 miles (11 km). FYI: Distance in the Grand Canyon is utterly deceptive. By comparison, a mile here is like five, six or seven miles anywhere else. Hence, the rule of thumb when hiking in the Grand Canyon is to gauge distance by time, not mileage. (See Part II for more background information on hiking trails in the canyon.)
The average North Rim trail from rim-to-river is around 20 miles (32 km). The disparity of trail length is caused by the river cutting its way into the former Kaibab Plateau region on the southern flank of the future canyon in the making. It follows how the initial breach was far to the south, thereby making two uneven parcels. The North Rim side of the canyon is also eroding more quickly compared to the South Rim. That side of the canyon, therefore, receives more moisture (because it’s higher). Besides, there are more streams flowing on that side of the river.
Flora-Fauna: Grand Canyon’s impressive roster of life forms include 373 bird species, of which some 290 live inside or on the rim year-round; 91 mammals; 17 fish species; 57 reptiles and amphibians; 37 mollusks; 33 crustaceans; 8,480 invertebrates; an infinite number of insects, some 1,750 plants; 64 moss species; 195 lichens; and 167 fungi. Of the 34 mammal species found along the Colorado River corridor, 15 are rodents and 8 are bats (i.e., the smaller variety, like pipistrelles and mouse-eared). Of the eight native fish species found in the river before 1963 (when the Glen Canyon Dam was in operation), 3 are now extirpated (absent from the record). Trout and catfish have since been introduced because the former and relatively warmer water has become dam controlled and cold, thereby dramatically altering the inner canyon ecology.
The diverse variety of life forms exists here because there are six types of vegetation formations from rim-to-river: riparian, desert scrub, piñon (Pinus edulis) and juniper (genus Juniperus) woodland, ponderosa pine forest (Pinus ponderosa), spruce/fir forest and montane meadows/sub-alpine. Additionally, part of the reason for such biodiversity relates to three desert environments and their respective, and different, ecosystems that merge at the bottom of the canyon: the Lower Sonoran ecozone, and the two encroaching deserts, the Mojave from the western sector and the Great Basin from the eastern sector. The Colorado River is the main access route that not only divides the North and South Rims, but also the eastern and western sectors. Each desert environment ushers in its native plants and animals, at least, in part. All three desert ecozones, therefore, contribute to a wealth of life forms throughout GCNP, especially inside the canyon's high-walled province.
Because Ecozones (aka “biotic life zones”) change so quickly, as well as a limited amount of distance, flora, and fauna comprise another lengthy roster of animals, avians, and plant life species living inside the canyon or on the rim. Hiking into the canyon, where each average step takes hikers back in time some twenty thousand years, is, therefore, comparable to undertaking a journey from central Canada to central Mexico. However, here the difference of life zones is achieved in under 10 miles (16 km) from the South Rim! Life forms adapt to various ecozones. Moreover, ecozones are primarily governed by temperature gradient and aridity factors.
Because it’s hotter and drier as the canyon deepens, plants, like animals, birds, and insects, must also adapt and change to such extremes. Thus, surviving as drought-resistant species. There's also a usually 25 or 30-degree average difference in temperature on sunny days from rim-to-river. Naturally, snow and ice at the bottom of the canyon are exceptionally rare. The snow line also seldom goes below the Supai or Redwall Formations (respectively the fifth and sixth major layers below the rim).
Historically, the South Rim recorded an average of 60 inches (152.4 cm) of snow a year while the North Rim recorded 180 to 200 inches (457.2 to 508 cm). However, these figures are pre-drought estimates before the 1990s. Since then, a reasonable statistical average is about a third of the original measurement. At the bottom of the canyon, say Phantom Ranch in the central corridor, the average precipitation is presently somewhere around 8 inches (20.3 cm), although parts of the canyon in the western sector receive as little as 4 to 5 inches (10.2 to 12.7 cm).
Names of the Grand Canyon's formations from the rim to river are as follows:
KAIBAB Limestone ... TOROWEAP Sandstone and Mudstone ... COCONINO Sandstone ... HERMIT Shale ... THE SUPAI GROUP (four distinct ledges and slopes made from mudstone and sandstone) ... REDWALL Limestone ... TEMPLE BUTTE Limestone ... MUAV Limestone ... BRIGHT ANGEL Shale (which covers the greenish and undulating TONTO PLATFORM stretching east and west below Grand Canyon Village) ... TAPEATS Sandstone (the first and oldest sedimentary layer capping the darker, metamorphic rocks of the Inner Canyon Gorge). The VISHNU SCHIST makes up the bulk of the basement rock formations, with occasional outcroppings of the GRAND CANYON SUPERGROUP rocks.
The upper two-thirds of the Grand Canyon layers account for the Paleozoic Era (541 to 254.2 myr). Both aquatic and terrestrial species emerge during this time. However, and for the most part, creatures were spawned from a variety of seas and a quiet ocean or two. Because the upper formations are strictly Paleozoic Era formations, one, therefore, does not find dinosaur fossils in the formations. The reason is because their species did not appear in the roster of life forms until the next era, the Mesozoic (252.2 to 72.1 myr). Think of the Paleozoic Era as life-friendly to aquatic species and the Mesozoic Era as life-friendly to reptiles and birds; also, insects, spiders, and a lush variety of verdure.
The Grand Canyon features a shapely canyon-wall facade because of what geologists refer to as differential erosion. Namely, hard rocks tend to form cliffs while relatively softer rocks form slopes or ledges. For example, the Kaibab Limestone and Coconino Sandstone (respectively the first and third major formations starting from the rim) denote a cliff-like profile while the Hermit Shale and Supai Group (respectively, the fourth and fifth major formations below the rim) typify a slope-ledge profile. If these upper layers were not a variety of sedimentary layers, and were one basic type of rock layer instead, say, limestone, then the profile of the canyon walls would be one massive cliff from top to bottom.
A number of environments account for the upper canyon formations: seas, swamps, rivers, mudflats, lagoons, even a Sahara-like desert (i.e., the Coconino Sandstone formation). Some fifteen encroaching and retreating seas occurred during the Paleozoic Era’s depositions. It follows how most of these environments were aquatic, either saline or clear-water seas. Combined, the mix of terrestrial and aquatic environments came and went across the pages of time in this region because the North American tectonic plate was migrating northward (and still is). Inch-by-inch, the continental plate crossed latitudes representing various climatic zones (i.e., the Equator, Subtropics, Tropics and Temperate Zones). Thus, the upper formations deposited over millions of years reveal changing and matching select environments over this lengthy timespan, each connected with equally changing latitudes and climatic patterns. The tinctures in the canyon walls also correlate with a plate tectonic transition across latitudes and climatic zones since the breakup of the supercontinent known as Pangea (meaning, “one world”), which may have happened, or started to happen, some two-hundred million years ago.
The harder crystalline (metamorphic) rocks formed in the inner canyon gorge, and usually revealed as dark-colored rocks, are remnants of an ancient mountain range––the Vishnu Range by name. This part of the canyon's V-shaped interior also represents the Precambrian Era (dating back some two billion years).
In select sectors of the Grand Canyon, later Precambrian sediments swept into the region, then dried out, congealed, and were deposited (stacked) on top of the original (basement rock) foundation. These sedimentary materials mark the multihued Grand Canyon Supergroup layers, whose askew formations were later subjected to force, heat, and pressure. In more descriptive terms, this phase of the Grand Canyon’s creation entails a fault-blocked mountainous event caused by a reverse fault (stretching) of its entire foundation. Ergo, a geophysical event caused by the movement of large crustal blocks when potent forces in the Earth’s crust pull it apart. Consequently, the Supergroup layers are tilted some 15º (to as much as 20º) toward the northeast. These singular-looking and easily distinguishable outcroppings are best seen in the eastern sector below Desert View. However, across from Grand Canyon Village, on the north side of the canyon, there is what is called an island showcasing a part of the Supergroup foundation. The island is just above Phantom Ranch and opposite Plateau Point, 1.5 miles (2.4 km). This popular hiking destination is due north from Indian Garden (an easy hike from the ranger station and campground). There are also similar islands in the park though this prominent display opposite Plateau Point is the most conspicuous. The easiest explanation for why and how the Supergroup layers appear is because the first Cambrian Period seas that inundated this region were lower than the much older and higher island sectors, and, therefore, incapable of covering up the Supergroup layers. This explanation is not the case in the eastern sector, however. In this quadrant, the formations are entirely askew. Hence, distinctive in both their color and profile. It also follows remnants of the Vishnu Mountains do not extend that far east.
There are about nineteen major and mixed sediments from the rim to the bottom of the canyon. The upper formations are sedimentary formations (i.e., mainly the more common limestone, sandstone, and shale or siltstone variety). All these materials represent the changing environments of geologic history––the Paleozoic Era phase. Sedimentary rocks are, therefore, the most common rocks of the Grand Canyon’s overall geologic makeup. For a convenient breakdown list, think of limestone formed from the calcareous skeletons of organisms such as corals, mollusks, and foraminifera; sandstone forms from clastic particles, mostly quartz or feldspar; siltstone; mudrocks form from shale, silt, and claystone particles; and conglomerates are composed of rounded gravel and breccia, meaning composed of broken fragments of minerals or rocks cemented together from the composition of their fragments.
The Precambrian Era is typically metamorphic rocks (i.e., a new blend of rock material from older components), and some that are sedimentary or metasedimentary, the latter altered by metamorphism (i.e., both types classified as Grand Canyon Supergroup rocks). Beneath this hard rock foundation is the third classification of rocks: igneous. Their materials originated from a reservoir of magma (what geologists dub a “batholith”). This much hotter source of materials eventually broke through the surface and injected newer (i.e., younger) material into older rocks, which is further defined as intrusive dikes-and-sills of intrusions. Geologically, dikes squeeze across layers of sediments while sills squeeze between the layers.
An additional note of interest in the Grand Canyon's upper layers is that the original formations in this region were estimated to be some 4,000 to 8,000 feet (1,219 to 2,438 m) higher than what is presently seen. Composed of relatively softer sediments deposited during the Mesozoic Era (252.2 to 72.1 myr), these materials are mostly derived from shale, siltstone, and sandstone, and were quickly eroded. Hence, the reason the additional accumulations were removed, leaving a hard-capped limestone on both rims. It’s this type of harder rock formation (the Kaibab layer) that preserves today’s Grand Canyon's formations below the rim (that is for now)!
The Precambrian Era of the inner gorge entails two long phases of the Earth’s geologic history: the Hadean and Archean Eons that lasted up to some 2.5 billion years ago. Then began the younger geologic eras, starting with the Paleozoic Era. Spanning from the beginning of the planet’s formation around 4.5 billion years to the start of the Cambrian Period (541 to 489.5 myr), the Precambrian Era represented in this region makes the Grand Canyon the largest repository of the oldest exposed rocks in America.
Additional Background: The oldest rocks in North America are found in the Superior Upland region, which is part of the Canadian Shield geologic province. Generally, the rocks date from 2.6 to 1.6 billion years ago. However, the oldest rocks on the planet are between 2.5 and 3.8 billion years ago, and can be found in the Acasta Gneiss of the Slave craton in northwestern Canada. This region displays ancient rocks in the Nuvvuagittug greenstone belt on the coast of Hudson Bay in northern Quebec. Scientists use isotopic dating methods to determine such ages, analyzing the decay of the radioactive element Neodymium-142 contained within the rock samples.
A summary of the planet’s rock chapter eras are the Precambrian Era (Hadean, Archean, and Proterozoic Eons) that roughly began some 4.5 Ga (billion-year symbol); the Phanerozoic Eon entailing the Paleozoic Era (541 to 254.2 myr), sometimes referred to as “Early Life” (or Age of Fishes); the Mesozoic Era (252.2 to 72.1 myr), sometimes referred to as “Middle Life” (or Age of Reptiles); and the ongoing Cenozoic Era (66 myr), sometimes referred to as “Recent Life” (or Age of Mammals).
Returning to the original foundation of the Grand Canyon’s materials, the first phase of its ancient rock foundation was laid down sometime between 1.8 (or 1.7) and 1.2 billion years. The clock of time thus begins when metamorphism begins, which does not include the original gathering of its primal materials that may have been some 5 miles thick (8 km) of sedimentary materials on the sea floor in this region. During this period, the Vishnu Mountains were created, and may have been a mile or so higher than today’s Rocky Mountains. The soaring Vishnu’s all-black range (hence, a mostly micaceous foundation of schist) were subject to erosion and eventually eroded to mere roots (called a peneplain). Some time after the wholesale leveling of the mountain range, say, around 1.2 billion years, Precambrian Era sediments washed in and stacked up one after the other. These, the previously mentioned Grand Canyon Supergroup formations, lasted until about 600 to 700 myr. Around 541 myr, the Precambrian Epoch came to an end and was geologically updated by the tripartite eras of the Phanerozoic Eon. Hence, the rock chapter formations, starting with the Paleozoic Era.
Where the Precambrian foundational layers end and the Cambrian Period begin is the previously mentioned Great Unconformity (i.e., where the summit of the eroded Vishnu Mountains meets the first sea of the Cambrian Period known as the Tapeats Formation). Another unconformity also exists where the Supergroup rocks come in direct contact with the Paleozoic Era’s Cambrian Period. Hence, the missing rock register begins sometime after 1.2 Ga (representing about 600 million years), whereas the original, and greater, unconformity begins at 1.8 billion years, therefore, defining a benchmark of 1.2 billion years.
Taking this claim one step further, among the many periods of the Paleozoic Era, two important periods are missing: the Ordovician (485.4 to 445.2 myr) and Silurian (443.4 to 423 myr). Both periods represent episodes of lesser unconformities. Whatever happened––as geologic and environmental events––during these missing benchmarks is subject to conjecture. About the only part of the mystery that is known is that these respective periods and their depositions are obviously not present in the Grand Canyon. The same claim holds true for the entire State of Arizona. It follows how the Paleozoic Era’s representative Cambrian, Devonian, Carboniferous periods (i.e., the Mississippian, Pennsylvanian), and Permian Period defines the formation layers from the first to last Paleozoic Era Grand Canyon depositions. What could be the reason for the two missing periods? Possibly, the region’s environs were too high and dry, which means there was no deposition material left at that time. Another possibility is that the formations were deposited, and then quickly eroded away. The conspicuous absence of these two major periods, therefore, typifies another Grand Canyon mystery added to a small list of unknowns. Otherwise, the academics of geology over the past century have made great strides given the known factors affecting this domain, as well as the larger domain its estate is part of––the Colorado Plateau Province.
As previously noted, there are other unconformities in the upper canyon walls. These types of unconformities all vary in missing years (as primary benchmarks), as well as types of unconformities. For instance, the contact between the Precambrian Supergroup and the Tapeats Sandstone is an example of an angular unconformity. Compare this type to so-called disconformities representing periods of non-deposition, where the layers above are parallel to the rocks below the unconformity. Another type, the nonconformity, occur where the Precambrian Vishnu Schist comes in direct contact with the Supergroup layers and Cambrian Tapeats Sandstone. Remarkably, the Grand Canyon’s geologic textbook represents the most extensive rock repository record on the planet; at least, this is true for its Paleozoic Era display. However, with all the unconformities in various periods, there is more here that isn’t seen than what is seen!
The final point about these mentioned highlights comes down to a subject question for readers to
decide: What makes the Grand Canyon so appealing to the eye? Is it the geology of its makeup?
The diversity of the canyon’s numerous life forms, and what some people go so far as to think is
a wasteland, only to find out the desert environs below the rim is anything but a wasteland. That
being said, is it the sheer size and magnitude that make the Grand Canyon’s abyss so
overwhelming, both in form and the immensity of its void? Whatever the viewer thinks and feels
is, of course, the right response. Suffice it to say how the next part of the text describes what
other historical people thought about this region and the epic chasm beyond the view from either
rim. For visitors today, here is indeed a cavernous landscape where superlatives go to die; where
all the adjectives one can think of are sorely lacking. Surprisingly, there were people here long
ago who were utterly disgusted with the canyon. Thus, everything, in the way of sentiment,
comes down to what people in the past thought about the canyon’s utility––and, therefore, not
just the aesthetics we revere today.
A Parting Reminder: The Grand Canyon’s creation story, as a formula, amounts to this numbered sequence of events:
The materials were laid down over some two billion years; the accumulations were more or less in storage for millions of years; and the stupendous uplift of the Colorado Plateau caused by plate subduction happened sometime between 70 and 30 myr. This best guess estimate will have to do for now. Likely, the geophysical event happened slowly though not all at once. Therefore, and given the timing of the overall uplift, three or four pulses (stages) are suspected. Amazingly, the landscape mostly stayed intact. In other words, the geologic record was not destroyed and the geologic book that was later revealed by erosion reads accurately.
In time, a catalyst came along, which for now can be thought of as the Colorado River; that is keeping with the traditional (theoretical) explanation of this drainage opening up this virgin territory. Once the river’s groove was deep enough, and layers below the upper crust were exposed, the physical and chemical elements of erosion set in and began to sculpt the exposed layers, helped along by faulting and gravity. Ergo, a veritable canyon in the making.
Based on the Grand Canyon’s age of its materials, at some two billion years, the surprising answer to its relative youthful fabrication stuns most people when they hear it: a mere five to six million years! The rest of these details will be fully explained in part three; also, another popular theory with another drainage taking the credit as the real initiator of the Grand Canyon project.
Bonus Details For Trivia Buffs: The Grand Canyon is considered the most sublime canyon in the world. It's also one of the deepest chasms. However, the deepest canyon may be the Yarlung Zangbo or “Tsangpo”), which is along the Yarlung Tsangpo River in Tibet. It’s also slightly longer than the Grand Canyon. There are other rivals that may also get the nod for lowest elevation in the literal shadow of the Himalaya Mountains. Then again, due to the inaccessibility of some major canyons tucked away in this part of the world, these deep gnashes in the planet’s crust are not regarded as candidates, much less rivals.
For example, the Kali Gandaki Gorge or Andha Galchi, where the Gandaki River flows through towering granitic walls. This impressive gorge area separates the major peaks of Dhaulagiri (26,795 feet/8,167 m) to the west and Nepal’s Annapurna summit, rising 26,545 feet (8,091 m) in the east. The difference between river elevation and peak elevation is also greater here than anywhere else in the world. The surging river of mostly whitewater also flows at elevations lower than the peaks between 4,300 to 8,500 feet (1,300 - 2,600 m) and 18,000 to 22,300 feet (5,500 - 6,800 m). Do the math!
Apart from the depth factor, the Grand Canyon is not the widest canyon. That record goes to Capertee Valley in New South Wales, Australia, about 0.6 miles/1 km wider and longer than the Grand Canyon. About a 2.5 hours drive from Sydney, Capertee Valley is no rival to the Grand Canyon regarding spectacular scenery and geology. There's also another rival, Mexico’s Copper Canyon, with six distinct canyons in the Sierra Tarahumara, which is located in the southwestern part of the State of Chihuahua. It’s also claimed that part of Copper Canyon has a nexus which is 1,000 feet (304 m) deeper than the Grand Canyon.
Although some of these record-breaking locales probably do rival the deepest and biggest canyons in the world, what sets the Grand Canyon apart from all other challengers is the way its domain has been fashioned. Thus, a series of mini-canyons with drainages and all within the greater context of a mother canyon. Certainly, with its near naked walls and multihued bands of numerous formations, whose overall profile creates a sensational visual backdrop, the Grand Canyon is the most appealing chasm on the planet; at least, most people think this boastful statement is true.
In the next installment of this three-part special series, the other facets of the Grand Canyon will be explored. Namely, the natural and human history. Featured hiking trails will also be included. The final segment’s focus on the creation story will be presented in its near entirety (read, “a cursory explanation of the highlights”).
(end Part I)