Prologue: I have been asked numerous times, and here I'll paraphrase the gist of those comments, "Rich. . .since you often refer to the Grand Canyon as your 'other' office, why don't you take us on a tour?" To tell you the truth I don't have an explanation, other than I have been preparing a special 10-part series on this 'other' office I've come to know since 1970, but lately decided I'm not sure if the DKos audience has the patience to sit thru all that reading. This is, after all, first and foremost a politically-oriented site, and I am very grateful to have garnered a niche market audience given the national parks, monuments and archeological ruins tours, with an emphasis on a staunch environmental endorsement for such protected places (including all other rare and vanishing open spaces). That being said, I decided to liberate the Grand Canyon tour from the larger copyrighted (my own) tome, FAMOUS LANDMARKS OF THE SOUTHWEST (which I hope to eventually pitch to a publisher). For this illustrious audience, you folks, I have somewhat downsized the original information into more compact diary formats (I know, what you have been getting in these tours is anything but compact).
On that note, may I remind all of you the innovative format of these diaries replicates the series, in that the information shared in the guise of a virtual tour is layered. Thus going from the basic to more comprehensible, where the reader gets to decide how much or how little to read. Moreover, all the diaries tend to focus on three main themes as subject matter: geology, natural history (flora and fauna), and human history relative to the site that is featured. It follows some people are not interested in all these facets. Ergo, one reads what one is interested in reading.
Finally, because the Grand Canyon is such a huge chasm featuring so much background information, its knowledge requires a two-part series. Indeed, there also be a special addenda immediately following the final presentation with a focus on hiking trails on both sides of the canyon. In this lengthy list will be a trail description of the most popular hiking, the Bright Angel Trail which extends from the South to the North rims (and changes name to the North Kaibab Trail on the other side of the Colorado River).
Now let's get started on tour of the big ditch of northern Arizona. She may not be the biggest canyon in the world, but by God she's the best. I also refer to this chasm in such a personal way because She really is the Mother Canyon of them all!
Location/Geography: In north central Arizona, Coconino County. Closest city: Flagstaff. Area: 1,217,403 acres (1,904 square miles). Colorado Plateau physiographic province. Kaibab Plateau region that was broken apart millions of years ago and dissected into seven major slices: the Marble (canyon) Platform; the North Rim's Kaibab, Kanab, Unikaret, Shivwits; and the South Rim's Coconino and Hualapai Plateaus.
Note: All photos posted in this and the following diary are my own or contributed by former Grand Canyon Field Institute or Northern Arizona University students (unless otherwise specified.)
Spotlight: A nearly two billion-year rock repository of materials created in the last five to six million years. A process of uplift and downcutting, followed by erosion. There are two versions of the canyon's creation: The first is the easiest, dubbed the fairytale version, meaning the Grand Canyon was entirely created by the Colorado River. The second version requires additional thought and explores the most popular theories pertaining to the Grand Canyon creation story (presently, there are two or three passionately discussed and defended by Colorado Plateau geologists). Meanwhile, the cause and effect aspects of the Grand Canyon is fairly easy to comprehend and has everything to do with downcutting (by the river) into a former intact plateau landscape by which all else followed.
Snapshot: Grand Canyon NP (GCNP), entirely within the State of Arizona, is nearly 300 miles long, with an average 10 mile wide. It is not the deepest canyon in the world, though certainly the most sublime. Originally, Marble Canyon (an annex canyon just below Lees Ferry near Page, Arizona) was not originally included in the park's dimensions. However, today's GCNP includes Marble Canyon's 60-mile annex which ends where the Little Colorado River merges with the Colorado River (at mile-60). The LC, as the Little Colorado River is commonly called, is the only major tributary feeding into Grand Canyon's province. President Theodore Roosevelt first visited here in 1903 and sought national park protection for the Grand Canyon. However, he achieved only Congressional approval for a game preserve status which happened on November 28, 1906. Later, on January 1, 1908, he added national forest lands along the rim that changed the preserve status to a national monument. Although he tried for many years for the coveted protection of a national park status, his request was denied for many years. Then on February 26, 1919, President Woodrow Wilson made it official: Grand Canyon became a national park.
Guided Tour Essentials: Because the Grand Canyon entails a lot of facets of knowledge and explanation, what follows in this presentation is longer and more entailed. Suffice it to say only some of the basic facts are covered, such as the pertinent facts listed below, as well as a viable explanation of the what-where-how-why-when behind the Grand Canyon's creation story. For example, this chasm in northern Arizona is about time, erosion and materials. Once the materials were laid down, it took X amount of time to create this natural wonder. The process entailed, first, an accumulation of materials over hundreds of millions of years, then a great uplifting of the earth’s crust (the Colorado Plateau in its entirety), followed by downcutting by the river. Finally, elements of erosion, assisted by faulting, hones the canyon’s profile. Although the materials at the base of the canyon date back some two billion years, the process of erosion actually took place fairly quickly. Indeed, from just five to six million years. What follows is a mere explanation of the nuances, however simplistically stated regarding these salient points.
Making A Canyon ‘Grand’: What makes the Grand Canyon so grand chiefly has to do with the canyon’s dimensions and stunning profile of geologic features. This leviathan of nature occupies a large physical space outlining its boundaries. The length is measured from Lee's Ferry below the Glen Canyon Dam (a 14 mile sinuous annex corridor). This historic setting is designated “mile-0” of the Colorado River’s run through the Grand Canyon to the Grand Wash Cliffs at the western sector: 277.7 miles. The width varies anywhere from 4 to 18 miles, with an average width of 10 miles thus defining the central corridor below Grand Canyon Village. At nearly 6,000 feet deep, the Grand Canyon is one of the deepest in the world. The opposing rims are capped with the same hard limestone, thus preserving the integrity of the walls. The South Rim elevation is an average of 7,000 feet above sea level, while the North Rim averages 8,000 feet. The peak elevation is 8,900 feet in the eastern sector but dropping to an average of 4,000 feet lower in the western sector. The main contrast between the rims on either side of the Colorado River is climate which entails the change and adaptation of flora and fauna. The North Rim receives most of the precipitation, both rain and snow, while the western sector (on both rims) receives much less.
As the raven flies from the central corridor, it's an easy 10 mile flight from the South- to North-Rim. Hiking the Bright Angel trail, which connects to the North Kaibab trail on the other side of the river, is 24 miles. However, by road it's a staggering 225 miles. Of the two rims, the South Rim receives more visitors chiefly due to its accessibility close to the I-40 corridor. More importantly, the South Rim is opened year-round and offers more tourist amenities (hotels, shops and restaurants). The North Rim is by far the more remote locale and is not favored by a close proximity to major thoroughfares or an abundance of tourist amenities. It’s less crowded domain is also closed from around mid-October to mid-November, typically due to heavier snowfall.
Note: The persistent drought throughout the Southwest for some twenty years has reduced snow accumulation by at least thirty-five percent, and in some years a greater percentage.Like A Gigantic Marble Cake: For most people, the Grand Canyon’s most famous characteristic comes down to its geology and fashioning. This is no ordinary V-shaped canyon such as others like Hells Canyon in Idaho or the Black Canyon of the Gunnison in Colorado. The stepped walls here defining an unusual profile is only part of what makes the Grand Canyon the marvel that it is; and great enough to be called The Natural Wonder of the world. The Grand Canyon is also designated a World Heritage site. The easiest way to understand the foundation of this extraordinary creation of nature is to think of a cake, a very large cake, with many distinct and tinctured layers of varying sedimentary material. The upper walls of the canyon are stratified––laid down one by one––with the oldest formations stacked at the bottom. These layers rise above the deeper V-shaped gash of the inner canyon gorge, where the Colorado River works the bottom of the canyon. Each layer also represents different environments (dry, wet and in between). Roughly, the Grand Canyon cake above the gorge began 540 million years ago, representing different formations from the Paleozoic Era (540 to 250 million years). One might also say this geologic textbook era marks the time when life forms first appeared on the planet, early life forms mostly spawned in shallow oceans. The layer capping both rims is the end of this great life-giving era.
The materials of the Grand Canyon cake-layers consist of limestone, sandstone, conglomerate (or siltstone) and shale, all sedimentary rocks. These horizontal formations create the upper two-thirds wall of the canyon with its telltale cliff-slope-ledge profile. Below the profile the inner canyon takes on a predominant vertical appearance. Down there in the basement are metamorphic formations (meaning new rocks from old materials). This hard-rock formations mostly signifies the remains of an ancient mountain range, the so-called Vishnu Mountains, long ago eroded. These leftover materials denote the Precambrian Era (whose timespan is about 4.5 billion to 540 million years). The basement rocks (i.e., "deep time") are also nearly half as old as the planet, roughly going back nearly two billion years, deep time in the lingo of geologists, and possibly a lot older. Like a Precambrian Era pedestal beneath the upper horizontal cake layers, the much younger rocks of the Paleozoic Era are neatly stacked on top. Thus there is the image of a mountain range (the vertical profile) and a cake (the horizontal) that describes a disparate metaphor of the Grand Canyon’s structural features. The vertical is the darker and sinuous gorge slicking through the more colorful layers on either side. This presentation of the two distinct rock formations, the oldest being vertically placed and the youngest laid over the rind, is that two utterly and distinct geologic phases are part of the Grand Canyon's base materials. Roughly, a span of some 2 billion to 600 million years at the very bottom (representing the longer Precambrian Era), and the much younger sedimentary rocks of laid down on top, which began about 540 million years ago. There is admittedly an obvious discrepancy in the timeline (well, let's just say it's obvious to some), meaning missing rock formations, which will be discussed further along.
Note: The geologic timeline of the planet is divided into eons, eras and periods. The following guidelines are therefore presented to the reader to help keep track of how the Earth's geologic clock of time works, thus defining this trinity of age classification:
• CENOZOIC Era (Chapter V: "The Modern Age"):
Quaternary Period 2 my (i.e., millions of years ago)
Tertiary Period 65- 2 my
• MESOZOIC Era (Chapter IV: "The Middle Age"):
Cretaceous Period 145 - 65 my
Jurassic Period 210 - 145 my
Triassic Period 245 - 210 my
• PALEOZOIC Era (Chapter III: "The Early Age"):
Permian Period 285 - 245 my
Pennsylvanian Period 320 - 285 my
Mississippian (Carboniferous) Period 360 - 320 my
Devonian Period 410 - 360 my (partially missing in
the Grand Canyon)
Silurian Period 440 - 410 my (missing in the Grand
Ordovician Period 505 - 440 my (missing in the Grand
Cambrian Period 550 - 505 my
• PROTEROZOIC Eon (Chapter II; Precambrian): 2,500 to 570 my
• ARCHEAN Eon (Chapter I; "In the beginning"): 4,000 to
• HADEAN Eon (the time of "Hades"): 4,600 to 4000 my
The Paleozoic, Mesozoic, and Cenozoic Eras are also collectively referred to as the “Phanerozoic Eon,” which entails the much shorter segment of Earth’s recorded geologic record.
Note: For a more background on geology and geologic dating, please see and read this diary that was posted earlier:
Fundamental Facts: Before considering the elemental theory about why and how the Grand Canyon was created, here are some relevant details about the canyon apart from its staggering dimensions. These are also the kind of fact most people are curious to know, some of which have already been explained earlier:
1. Lee's Ferry (sometimes written "Lee Ferry" or "Lees Ferry") is the originating point for whitewater rafting through the canyon, also the beginnings of GCNP. This historic Mormon site is about 14 miles below Lake Powell's Glen Canyon Dam. At the western end of Grand Canyon lies the other large artificial oasis, Lake Mead. When this basin was full sometime in the 1970s, Pearce Ferry (sometimes spelled "Pierce") was the takeout point for Grand Canyon river runners (in some circles, affectionally called river rats). However, since then lake levels have steadily and dramatically dropped due to extensive periods of drought, the longest lasting being some twenty years (and holding). Thus Pearce Ferry has been high above the river's course for many years and now overlooks the lake from afar. In recent years, it was decided the better (and closer) takeout point is some 60 miles miles upstream at Diamond Creek (mile-232 down-river mileage from Lees Ferry). This convenient takeout point is located on the Hualapai (pronounced "wal-la-pie") Indian Reservation, about 22 miles from Peach Springs. This last segment of the Grand Canyon can still be rafted as a day trip operated by other commercial river runners. However, it requires extra time motoring downstream on Lake Mead to the nearest takeout point near Meadview AZ (South Cove). There's also the option of a shorter and more popular excursion below Grand Canyon West (about 40 miles downstream from Diamond Creek), then taking a helicopter to the rim. This rafting-helicopter lift out concession is also managed by the Hualapai Tribe. (Note: Sometimes the weather is not cooperative, necessitating boaters continue downstream to South Cove, making for a very long and scenic day on the river and lake.)
2. The Colorado River below Grand Canyon Village is 2,400 feet above sea level. Along its 1,450-mile cascade 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 trapping of its resource), the Colorado cuts and carves a series of deep canyons, as does its sister drainage, the Green River. The Colorado River drops in elevation some 2,000 feet inside GCNP, creating nearly one hundred and twenty fair-sized to major rapids (not counting some sixty other minor rapids). Some forty to sixty of the rapids are gnarly whitewater, rated Class V (with Class VI considered non runnable). The number of highest-rated rapids also varies and depends on the level of c.f.s. (cubic feet per second). Some rapids either wash out in high or low water, or else worsen.
3. The average South Rim trail distance from rim-to-river is about 10 miles, which marks the central corridor. The shortest trail is the South Kaibab (near Grand Canyon Village) to the Colorado River, about 7 miles. (Note: Distance in the Grand Canyon is deceptive. By comparison, a mile here is like five, six or seven miles anywhere else. Thus, the rule of thumb when hiking the Grand Canyon is to gauge distance by time, not mileage.)
4. The average North Rim trail from rim-to-river is around 20 miles. 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 canyon. Think of the future cake being cut far to the south, thereby making two uneven parcels.
5. Grand Canyon's 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, 1,750 plants, 64 species of mosses, 195 lichens, and 167 fungi. Of the 34 mammal species found along the Colorado River corridor, 15 are rodents and 8 are bats (the smaller variety, like pipistrelles and mouse-eared). Of the 8 native species found in the river before 1963 (when the Glen Canyon Dam went into operation), 3 are now extirpated. Trout and catfish have now been introduced, because the former and relatively warmer water has become dam cold, as in dam controlled, thereby dramatically altering the inner canyon ecology.
6. The diverse variety of life forms exists here because there are six types of vegetation formations from rim-to-river: riparian, desert scrub, piñon/juniper woodland, ponderosa pine forest, spruce/fir forest and montane meadows/sub-alpine. Also, part of the reason for such bio diversity is that three desert environments and their ecosystems collide at the bottom of the canyon: the Lower Sonoran, 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 eco-zones contribute to a wealth of life forms throughout GCNP, especially inside the canyon's high-walled province.
7. Because ECO ZONES (a/k/a/ "biotic life zones") change so quickly and in a limited amount of distance, the changing flora and fauna comprise a lengthy roster of animal and avian and plant life species living inside the canyon or on the rim. Hiking into the canyon (where each average step takes a hiker back in time some 20,000 years) is comparable to a journey from central Canada to central Mexico. Here the difference of life zones is achieved in under 10 miles from the South Rim. Life forms change that dramatically by adapting to the various eco zones, which in turn mainly are governed by temperature gradient and aridity factors.
8. Because it’s hotter and drier as the canyon deepens, plants, like animals and insects, must adapt and change to such extremes. There's also usually a thirty degree average difference in temperature on sunny days from rim-to-river. Naturally, snow and ice at the bottom of the canyon is something exceptionally rare. The snow line also seldom goes below the Supai or Redwall formations, respectively the fifth and sixth major layers below the rim.
9. Historically, the South Rim receives an average of 60 inches of snow a year, while the North Rim receives 180 to 200 inches. 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, say Phantom Ranch, the average precipitation is presently somewhere around 8 inches, although parts of the canyon in the western sector receive as little as 4 to 5 inches.
10. Names of the Grand Canyon's formations from the rim to the inner canyon gorge 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 so-called TONTO PLATFORM; the greenish, undulating landscape 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 denotes the basement rock formations, with occasional outcroppings of the GRAND CANYON SUPERGROUP rocks.11. The upper two-thirds of the Grand Canyon layers account for the PALEOZOIC ERA (540 to 250 million years). This era is also known as Early Life, and more informally the "Age of Fishes," because most life forms began in primal seas.
Note: Because the Grand Canyon's upper formations are strictly Paleozoic, one does not find dinosaur fossils in these more ancient formations. Such creatures did not make an appearance until the next later era, the Mesozoic (250 to 65 million years ago).12. The Grand Canyon features such a unique and shapely canyon-wall facade because of a process called differential erosion. Namely, hard rocks tend to form sheer cliffs. For example, the Kaibab Limestone and Coconino Sandstone (respectively the first and third major formations starting from the rim). Relatively soft rocks tend to form slopes or ledges. For example, the Hermit Shale and Supai Group (respectively, the fourth and fifth major formations below the rim). Thus the cliff-slope-ledge profile of the upper walls accounts for various types of sedimentary rocks.
Note: The following geologic breakdown of different rock types will be helpful identifying the principle rock formations of the Grand Canyon's layers:13. The numerous environments account for the upper stratified formations: seas, swamps, rivers, mudflats, lagoons, even a Sahara-like desert (the Coconino Sandstone formation). Invading and retreating seas may number some fifteen different environmental events during the Paleozoic Era. All the environments came and went across the pages of time because the North American tectonic plate was migrating northward.
Geologists classify all rocks on the planet in three categories:
• IGNEOUS (Form from a melt, or magma, deep within the planet. Such rocks can be extrusive (volcanic) in origin or else intrusive.)
• METAMORPHIC (denote transformation of an existing type of rock. The process is called "metamorphism," meaning rocks that change in form.” Thus new rock material made from old.)
• SEDIMENTARY (Formations made from limestone, sandstone, shale and conglomerate. The latter consist of rounded fragments and are differentiated from breccias, which consist of angular clasts. Both conglomerates and breccia (i.e., rock composed of broken fragments of minerals or rock cemented together by a fine grained matrix) are characterized by clasts (particles) larger than sand (about .07 inches). Conglomerates further break down into siltstone, claystone and mudstone.
Note: Like all other continental plates, inch-by-inch our continental plate was mobile and crossed latitudes representing various climatic zones (the Equator, Subtropics, Tropics and Temperate Zones). Thus, the formations in the canyon walls reveal these changing environments over millions of years. The tincture in the canyon walls also has much to do with crossing various zones.14. The harder crystalline (metamorphic) rocks formed in the inner canyon gorge, usually revealed as darker colored formations, are remnants of an ancient mountain range, the Vishnu by name. This part of the canyon's V-shaped deeper interior also represents the Precambrian Era (dating back some two billion years).
15. In select sectors of the Grand Canyon, later Precambrian sediments swept into the region, then congealed and stacked on top of the original basement rock foundation. These added meta-sedimentary materials are the vivid and multihued GRAND CANYON SUPERGROUP rocks. Their compacted materials were eventually fault-blocked as the crust of the planet stretched (called a "reverse fault"). Consequently, the Supergroup formations are tilted some twenty degrees to the northeast, like leaning books on an askew library shelf. These outcroppings are best seen in the eastern sector below Desert View. Across from Grand Canyon Village, and on the north side of the canyon, there's also an island outcropping of these Precambrian formations high above Phantom Ranch (to the west), or just opposite Plateau Point, 1.5 miles, which is due north from Indian Garden (the ranger station and campground).
16. There are about nineteen major and mixed sediments from rim-to-bottom of the canyon. The upper formations are all sedimentary: limestone, sandstone, shale, and conglomerate (sometimes called siltstone or mudstone). These materials represent the changing environments of geologic history, the Paleozoic Era phase.
17. The Precambrian Era rocks below the layers are metamorphic (a new blend of rock material from older components). Beneath this hard rock foundation are the igneous rocks that once spawned a reservoir of magma (what geology call a batholith). The source of these igneous rocks eventually broke through the surface and injected newer (younger) material into the older rocks, defined as intrusive dikes-and-sills of intrusions. (Note: dikes squeeze across layers of sediments, while sills squeeze between the layers.)
18. An additional note of interest in the Grand Canyon's upper layers is that the original formations in this region were some 4,000 to 8,000 feet higher that what is presently seen. Those missing upper layers were composed of sediments deposited during the MESOZOIC ERA (250 to 65 million years), also known as the “Middle Life,” and popularly called the Age of Reptiles. However, there was no limestone in this material, which tends to erode much slower than other sedimentary rocks. Rather, the added accumulation was softer sedimentary formations, mainly conglomerate and shale. Consequently, these rocks were quickly eroded, eventually exposing the hard-capped Kaibab Limestone on both rims. It’s precisely this hard-rock cap foration that preserves the Grand Canyon's formations below the rim. For now, that is.
19. 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. Spanning from the beginning of the planet’s formation around 4.3 billion years ago to the beginning of the Cambrian Period (540 million years ago), the Precambrian Era represented in this region makes the Grand Canyon the largest repository of the oldest exposed rock in America.
Note: 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, which can be found in the Acasta Gneiss of the Slave craton in northwestern Canada. This region displays mega 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.20. The first phase of Grand Canyon's ancient rock foundation was between 1.8 and 1.2 billion years ago. During this period the Vishnu Mountains (probably a little higher than today's Rocky Mountains) were raised and eventually eroded down to their darkened roots (called a peneplain). Some time after their leveling, new Precambrian sediments washed in and stacked up one after the other. These, the aforementioned Grand Canyon Supergroup formations, lasted until about 600 million years ago. Around 540 million years ago, the Precambrian Epoch closed and was geologically updated by the PHANEROZOIC EON, combining the Paleozoic, Mesozoic and Cenozoic Eras.
Note: The Cenozoic Era began some 65 million years and continues to the present. Known as “Recent Life,” this era is commonly referred to as the Age of Mammals.21. Where the Precambrian rocks ends and the Cambrian Period begins is noteworthy to the trained eye. Millions of years of missing rock formations, called UNCONFORMITIES, reveal one of the other outstanding aspects of the Grand Canyon. Namely, there’s something like 1.2 billion years of missing formations from the rock registry. The geologic record is simply wiped out wherever unconformities are discovered. Most likely, these missing geologic pages were erased by erosion, and by some accounts the materials were never deposited.
22. Taking this claim one step farther, among the many periods of the Paleozoic Era, two important periods are missing: the Ordovician and Silurian (both therefore representing lesser unconformities). Whatever happened during this missing geologic record no one knows for sure. We only know their distinct materials are not found here, nor are these periods found anywhere in Arizona. Thus the Paleozoic's representative Cambrian, Devonian, Mississippian, Pennsylvanian and Permian Periods mark the way from bottom-to-top. What could be the reason for the two missing periods? Perhaps the environment was too high and dry, which means there was no deposition material left at that time. Another possibility is that the formations were deposited but quickly eroded away. With no trace of their being here, their absence is simply another Grand Canyon mystery to add to the list of unknowns. (How and where this region was originally cut and carved being the greatest mystery.)
Note: Just east of the scenes above, the Great Unconformity becomes deliciously complicated. A new set of rocks enters between the 'Vishnu' and the Tapeats -- the Unkar group of late preCambrian sedimentary rocks. In this scene are three of its formations: the Bass limestone, the Hakatai shale, and the Shinumo quartzite. These rocks were deposited at about ~1.1 billion years ago, ~600 million years after the Vishnu, and ~550 million before the Tapeats. Here, their western boundary is a fault (purple line with direction arrows), and they tilt down to the east (right). The Great Unconformity (red line) is above the Unkar Group, which is lies above a 'pretty good' unconformity (purple line) at the top of the Vishnu. To the west (left), the Tapeats is above the Great Unconformity. But, starting at the center mid-distance, the Tapeats thins to the east (right) and vanishes against the Unkar Group. The Shinumo quartzite pokes through the Tapeats and forms cliffs at the same elevation as the lower part of the Bright Angel shale (background center). In early Cambrian times, this Shinumo quartzite stood as a hill above the Tapeats sandy beach and the Bright Angel muds, and was finally buried in the mud as the sea level rose. (Excerpt liberated from http://www.lpi.usra.edu/...)23. Where the darker-colored walls of the inner canyon gorge abut directly against the brownish Tapeats Sandstone, the aptly named GREAT UNCONFORMITY appears. This missing benchmark in time was first named by the first river explorer through the Grand Canyon in 1869, Major John Wesley Powell. His discovery shows where the Precambrian rocks representing some 1.8 billion years abut against Paleozoic rocks laid down 541 million years ago. Thus a staggering 1.2 billion years of missing time. However, where the Precambrian Supergroup rocks (roughly a 1.2 billion to 600 million year span) appear above the Vishnu formations, the unconformity is lessened to about six hundred million years. These later Precambrian formations, appear as isolated outcroppings east of Desert View and therefore were likely quickly eroded away in most sectors (except near the central corridor, such as below the Grand Canyon Village sector). Those areas that were not eroded are referred to as islands, because the Supergroup formations were high enough not to be buried by the newer Paleozoic Era’s events.
Let The Questions Begin: Given these above facts, including the implied mysteries of missing rocks, how did such a place as this great Grand Canyon ever get started? The answer is found in uplift, in this case the uprising of the Colorado Plateau. However, no one knows for sure just when the uplift occurred, or if it happened in one pulse or several. It's generally assumed this epic event happened sometime between 70 and 30 million years ago. Indeed, the entire physiographic Four Corners region was affected by the uplift. Think of some 15,000 feet of layered materials raised about an average of 6,000 feet above sea level. The process is much like a sky island foundation of many plateau regions standing at different elevations. Sometime after the major uplifting event, the overall plateau province was downsized into various and smaller segments (plateaus became mesas, mesas became buttes and some buttes became hoodoos, spirals and pinnacles). This erosional downsizing happened because elements of erosion had fashioned the various sedimentary materials. Initially, it was streams and rivers that incised their way into the uplifted terrain, which is the only way downcutting takes place (meaning uplifted material that is simultaneously breached by downcutting streams and rivers). Most geologists are insistent about this fact. Simply put: Without uplift there can be no canyons. Hence, it took tandem uplifting, downcutting, and erosion to make the numerous canyons cut and carved into the rind of the Colorado Plateau. This geophysical force, as an event, is why vigorous rivers like the Mississippi or Ohio cannot incise canyons in their path.
The Colorado River, along with its sister drainage the Green River, are the primary agents that have scored a series of canyons into a relatively soft sedimentary skin throughout parts of the Southwest. The Rio Grande, San Juan, Escalante and Yampa Rivers, not to mention notable others, have also contributed to this sinuous process like delicate scrimshaw design viewed from high above the landscape. Once the breach into the upper crust of (mostly) Mesozoic Era formations happened, then wind, water, ice (during freezing months) and plants continued the fabrication process. Gravity and faulting abetted the process. Thus the Grand Canyon, along with other regional landmarks, were solely created because of the uplifting, downcutting and erosional processes. These processes continue to hone and refine the physiographic province that some claim is the most singular geology in the world––the Colorado Plateau. It should also be mentioned how having the right materials, in this case sedimentary rocks, along with an arid climate, works to the advantage of making an array of impressive canyons that are found in this quadrant of the Southwest.
Note: For a detailed summary of the Colorado Plateau, please see and read the following diaries:A Memorable Formula: An easy way to remember what happened here over the last sixty-six million years comes down to this template of nature: UPLIFT plus DOWNCUTTING, then EROSION over TIME. Let it also be said that what happens in one neighboring province also affects whatever landform is next to it. In this case, when the Ancestral Rocky Mountains (a/k/a/ the "Uncompahgre Mountains") were raised some 12,000 to 15,000 feet, the adjacent Paradox Basin (near present-day Moab, Utah) subsided. Additionally, in today's Basin and Range Province (the Phoenix region and extending westward into Nevada), what used to be the floor plan of the Mogollon Highlands, this locale’s raised outcropping of rock was initially destroyed by lowering the foundation (downdropped), then sometime after the great collapse the remains were eroded. This literal earthshaking and transformational event occurred at somewhat the same time the Colorado Plateau was raised.
Different kinds of geophysical events were therefore triggered by the creation and destruction of neighboring provinces. It's also the difference of elevation between the Colorado Plateau and other sectors, like the Basin and Range and the Rocky Mountains, that accounts for the distinct elevation extremes. The important aspect is how this land elevation difference explains how each topographical region was subsequently created. Think of it this way: mountain building destroys the geologic rock record (the destruction of the Mogollon Highlands as well as the raising of the Rocky Mountains), while the Colorado Plateau's creation maintains and keeps the rock record intact, simply because there's no mountain building associated with its creation; merely an uplift.
Bonus Details: There are many and various provinces throughout North America, each shaped by climate, materials and whatever geophysical forces, if any, traceable to the primal blueprint for that region. In the West, the Colorado Plateau and its adjacent neighbors (the Basin and Range Province and the Rocky Mountains) are each in concert with one another. For instance, varying elevations between each province determining which way water flows, just as the materials of each depends on how fast erosion takes place; also, helped along by prevailing climate. For the Colorado Plateau, and specifically the nature of this topic the Grand Canyon, a predominant arid climate has everything to do with how fast or slow the foundation of the Colorado Plateau erodes (but in this case the process is relatively fast). Remarkably, this explanation shows how the Grand Canyon was made grand (as a chasm fabricated by erosion) in as little as five or six million years. It may boast some two billion years of materials in the making. Yet the process of erosion that sculpted the features occurred, to use an apt expression, in the blink of an eye. There is also another benchmark of creation some geologists favor. For instance, the last body of water to inundate this region, the Mancos Sea, receded some eighty million years ago. This estimated figure may suffice as the latest possible date for the Grand Canyon to have begun its process of erosion and eventual canyon creation. However, the aforementioned five or six-million year estimate is most likely closer to a reliable timeframe for the Grand Canyon’s ultimate appearance. Still, the questions in most visitors minds when viewing this stunning spectacle of nature are:
1) How could some eight hundred cubic miles of materials erode in such a short time? and 2) Where did the material go?
Taking the second part of the question, and because it's the easiest to answer, gravity is the primary agent transporting spent material into the far inner reaches of the canyon. Eventually, the debris gets flushed out by the Colorado River, there at the western annex. Erosion, meanwhile, is the chief process that continues to turn rocks into clastic (particle) fragments. That's the nature of all sedimentary material: clastic particles originally congealed gradually breaking down into smaller units. These materials eventually empty into the river’s channel, which functions as a sluice. Yet the process doesn’t stop there. Erosion is ad infinitum in that its honing process continues wherever the river is flowing, in this case the Gulf of California. Of course, not all the material makes it that far; at least not since the damming of the Colorado began in the 1930s. Nevertheless, depositional material material found downstream from the Grand Canyon is transported by this sluice-like river; those materials that used to part of the Grand Canyon’s formations also match the origin of this environment. The methodology of comparing samples is also vital to geologists, because it’s the matching of materials (depositions) from one sector to another that confirms the science where the original stockpile originated.
I think this is a good place to stop and let you folks have a good ‘think’ on what you have learned thus far. Tomorrow’s continuing diary begins with a thorough explanation of the so-called fairytale version connected to the Grand Canyon’s creation story. Hope to see you on the tour.
So parting shots of wildlife:
And for the most common rascal above or below the rim, which you can take it from me is likely the most daunting of all pesky critters (when it comes to taking food right out of your hands). . .
I think this is a good time and place to take a break. So, let's continue the tour tomorrow morning and learn something new about this grand old place that has felt like home to me for over forty years.
As always, your thoughtful commentaries are welcomed.
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