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Pages of Stone: Geology of Western National Parks and Monuments: Grand Canyon and the Plateau Country
Describes important geological formations in sixteen national parks, discusses contintental drift, earthquakes, volcanic activity and erosion
158 pages, Paperback
First published June 1, 1988
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June 5, 2022
This was one of my first books about geology in short form, and it is still one of the best, setting the stage for the region and then narrowing into each monument and park and explaining certain places in each, a must have for trips to the region.
In less than 5 million years, Grand Canyon as we know it today, was excavated along the line established by the Ancestral Colorado as it curved southward around Mesozoic rocks on the highest part of the Kaibab uplift. Its gradient was increased by mountains and uplift of the Plateau entirely. Farther upstream the Colorado also deepened its canyon to create Canyonlands and western Colorado canyons like Glenwood Canyon.
In the Mesozoic Era, the land rose at the end of Paleozoic time and the western sea drained away. Mountains that had formed in Colorado and northern New Mexico in Pennsylvanian time shed sediments onto the flat Plateau region. Building floodplains and deltas. Now and then nearby volcanoes emitted volcanic ash. Well to the west, molten magma pushed up to form the granites of todays Sierra Nevada, a range that then as now cut off moisture swept eastward form the Pacific. A great Sahara developed across the Plateau region, its high-piled dunes giving us many of the scenery making rocks of the region. Just as today’s Saharan dunes creep across the Nile floodplain, the dunes of this ancient Sahara advanced across older floodplains, covering the soft, slippery river muds.
For nearly 200 million years, dinosaurs wandered across delta and desert until a shallow sea again swept this area, and large marine reptiles and elegantly spiraled ammonites swam above the fine gray mud of the sea floor. Toward the end of Mesozoic time, North America broke away from Europe and the newborn Atlantic Basin widened, and westward drift and collision with the East Pacific Plate caused new stresses in the crust. In the Laramide Orogeny, the present Rocky Mountains were born, rising east and north of the Plateau region and providing headwaters for the great Colorado River that, with its tributaries, would carve and chisel the landscape. During this time, the Colorado Plateau began to rise. The end of the Mesozoic Era may have been punctuated with great meteor showers, impacts of many asteroids, and airborne dust that led to the demise of more than half of the species of animals and plants then in existence.
On the Plateau, rock layers range in age from 600 million to a mere 6 million years are still in the horizontal position they were deposited in. Geophysical studies, which measure the thickness of the crust by the velocity of earthquakes waves pass through it, show that the crust is thicker under the Plateau than under surround areas, a factor that contributes to its raftlike integrity and longevity.
Red Canyon: these intricate mazes are sculptured in soft pink rock of the Claron Formation, made up almost entirely of limy Paleocene lake deposits that range from silty and sandy limestone to limy siltstone and sandstone with liberal doses of clay and volcanic ash. The pink color comes from minute amounts of iron oxides, mostly tiny grains of hematite. Red Canyon is pushed up 900 feet higher than Bryce and lie next to basalt dated at 500,000 years old. Paleozoic and Mesozoic layers have been eroded away, and thick layers of Cretaceous marine and near shore sedimentary rocks underlie the Claron Formation. As North American drew away from Europe at the end of Mesozoic time, the continent rose slightly, and the widespread sea in which the rocks were deposited withdrew. In the continental interior rose two ranges that play parts in Red Canyon and Bryce; the Rocky Mountains in Wyoming and Colorado and the Sevier Mountains in Utah. In landlocked basins between the two ranges, large lakes received runoff and finely pulverized rock debris from both. One of these inland lakes stretched diagonally across Utah from northeast to southwest, slightly larger than Lake Erie. In the lake in Paleocene time, silty limestone and mudstone lake deposits accumulated to depths a s great as 1000 feet.
From the ancient gneiss of the Inner Gorge to the white limestone of its rim, Grand Canyon unfolds 2 billion years of Earth history.
500 foot precipice gives its name to the Redwall Limestone, which is really gray but painted with an iron oxide wash from red slopes above.
One of the marvels of Grand Canyon is that it is here at all. Why should a river develop a course directly across a 9000 foot uplift? For the Colorado River bisects the very heart of the Kaibab Uplift, and bisects it so thoroughly that the river flows in desert summer while pine and aspen clothe the cool plateaus above, so thoroughly that animals south of the canyon have evolved differently than those north of the canyon…Regional drainage on the North Rim flows towards the canyon while that on the South Rim flows away from the canyon. The river is 4460 feet below the South Rim and 5940 below the North Rim, and the river is much closer to the South Rim than the North Rim.
In Grand Canyon, Precambrian rocks fall into 3 age groups; the highly metamorphosed Vishnu Schist which had its beginnings more than 2 billion years ago; granite that intruded about 1.75 billion years ago, and a younger group of sedimentary rocks. Studies of the schist show that it was involved in several pulses of mountain building and altered at depths as great as 12 miles below the surface. There was nearly a billion years of erosion in late Precambrian time-the longest, most widespread periods of erosion the Earth has known. Both older and younger rocks were trimmed away to an essentially horizontal peneplain expressed in the Great Unconformity between Precambrian and Paleozoic rocks, not only in Grand Canyon but in many other parts of the world. Recent studies in the Ozarks at the Great Unconformity there may show that the breakup of the ancient continent Rodinia that was uplifted which caused massive erosion.
Research shows that the Cambrian sea advanced in five pulses. Conglomerate and coarse sandstone near the shore, finer sandstone and mudstone further out, and finally limestone where the sea was fairly open. Toward the end of the Cambrian Period, the sea retreated and there is no record of Ordovician or Silurian time here. Either no deposits or it was eroded away. Some found in Ohio show there could have been extensive glaciation on Gondwana which exposed the rock to be eroded away.
The Redwall Limestone was deposited in Mississippian time; thick, strong, and extremely widespread, the limestone contains fossil fish and many small marine shellfish such as brachiopods, corals, mollusks, sea lilies and trilobites. It is bluish gray and stained with red iron oxide mud from the colorful shales above. The top of the Redwall Limestone is marked by erosion similar to that of many limestone areas today, a surface characterized by extremely irregular topography, with many caves, sinkholes and underground channels. This hummocky, irregular karst surface gives us a clue into the Mississippian climates here for such surfaces are known today in Kentucky, Puerto Rico, Slovenia, and other warm, humid climates.
The Supai Group and the Hermit Shale were deposited on a floodplain or delta and in an adjoining shallow sea, some of the rocks bear imprints of fernlike leaves and reptile tracks. A little later in Permian time, windblown sand swept across the Grand Canyon region, leaving a thick deposit of fine white sandstone marked with long, diagonal cross-bedding- the Coconino Sandstone, the white band on the canyon’s upper walls. Tracks and trails of lizardlike animals mark some sloping dune surfaces, but no bones or skeletons of the animals have ever been found. During the rest of Permian time, the western sea continued to fluctuate, twice it inundated the region, depositing the Toroweap Formation and the Kaibab Formation forming 500 feet of the upper canyon walls.
No Mesozoic rocks at Grand Canyon now, but those at Zion, Canyonlands, and Arches show thick layers of sand, mud and volcanic ash were deposited.
Gradual downcutting by the North Fork of the Virgin River shaped the Zion Canyon of today. The North Fork seems to placid to have accomplished all this erosion. But with summer thunderstorms or spring melting of snow on the Markagunt Plateau around its headwaters, the river picks up volume and speed, and pounds its bed with sand, pebbles, and even large boulders, cutting own at an average rate of 1 inch per century, 600 feet per million years. Canyon widening is the job of slides and rockfalls. The Kayenta Formation below the Navajo Sandstone is responsible for most slides; its relatively soft siltstones and mudstones fairly invite erosion.
As the Triassic Period began, this part of North America had just risen above the sea and was lying close to the equator, and formed a broad coastal plain sloping westward toward the ocean. Sluggish rivers wound across the plain, gradually depositing silt, mud and clay derived from the Ancestral Rocky Mountains. In mid Triassic times, the nature and source of the sediments changed. Coarse sands and gravel from highlands in Arizona formed the Shinarump Conglomerate. Still later, fine volcanic ash and mudflows created purple, green and gray layers that contain fossil amphibians and reptiles and make up the Chinle Formation. Coarse river channel and floodplain deposits formed the Moenave and Kayenta formations and indicated cessation of volcanism in late Triassic time. During the Mesozoic Era, North American slowly drifted westward and northeast. By late Triassic time, it had entered the dry subtropical latitudes, then as now the site of major deserts. On a wide, windswept Triassic-Jurassic plain, sand dunes piled up, layer upon layer, for millions of years. This sea of sand, stretching from northern Arizona to southern Wyoming, is now the Navajo Sandstone.
A few layers of red siltstone, the Temple Cap formation and above it are thinner crossbedded sandstone of the Carmel Formation show that the western sea briefly flooded this are near the end of the Jurassic Periods. Much later, in Cretaceous time, the sea advanced again, coming from the east. The Dakota sandstone is the youngest sedimentary unit and in remote areas. Marine sediments- fine gray shales, sandstone, and limestones fill out the Cretaceous sequence in other parts of the Plateau like Arches NP and Bryce Canyon But do not appear in Zion. Near the end of the Mesozoic Era, the Rocky Mountains rose was and norther of here stretching in a great arc from New Mexico to Canada and putting an end to the pulsing incursions of the sea. As the Rockies rose, deep intermountain basins in Utah and Wyoming began to receive rock debris form them. Lakebeds from them show up in Bryce, Cedar Breaks, Red Canyon. All tertiary in Zion have eroded away. Lava flows and cinder cones and evidence of Quaternary lakes with faults deep enough to tap the basalt magma of the Earth’s mantle, dated as 260,000 to 1.4 million years old. The primary geologic process of Quaternary time was and is erosion, the amount of erosion faster in Pleistocene time, when precipitation was greater than at present. About 4000 years ago, a rockslide occurred at the lower end of Zion Canyon, 1 mile above the bridge and junction of the highway routes into Zion. Damming the North Fork of the Virgin River, a long narrow lake existed for 1500 years.
Checkerboard Mesa is capped with striped layers of the Temple Cap and Carmel Formations on Navajo Sandstone, where water has incised small gullies along vertical joints while wind and blowing sand have etched the sweeping cross bedding of this rock.
The highway travels up Pine Creek Canyon and tunnels through Navajo Sandstone at the Kayenta (river and floodplain deposits) -Navajo contact.
In less than 5 million years, Grand Canyon as we know it today, was excavated along the line established by the Ancestral Colorado as it curved southward around Mesozoic rocks on the highest part of the Kaibab uplift. Its gradient was increased by mountains and uplift of the Plateau entirely. Farther upstream the Colorado also deepened its canyon to create Canyonlands and western Colorado canyons like Glenwood Canyon.
In the Mesozoic Era, the land rose at the end of Paleozoic time and the western sea drained away. Mountains that had formed in Colorado and northern New Mexico in Pennsylvanian time shed sediments onto the flat Plateau region. Building floodplains and deltas. Now and then nearby volcanoes emitted volcanic ash. Well to the west, molten magma pushed up to form the granites of todays Sierra Nevada, a range that then as now cut off moisture swept eastward form the Pacific. A great Sahara developed across the Plateau region, its high-piled dunes giving us many of the scenery making rocks of the region. Just as today’s Saharan dunes creep across the Nile floodplain, the dunes of this ancient Sahara advanced across older floodplains, covering the soft, slippery river muds.
For nearly 200 million years, dinosaurs wandered across delta and desert until a shallow sea again swept this area, and large marine reptiles and elegantly spiraled ammonites swam above the fine gray mud of the sea floor. Toward the end of Mesozoic time, North America broke away from Europe and the newborn Atlantic Basin widened, and westward drift and collision with the East Pacific Plate caused new stresses in the crust. In the Laramide Orogeny, the present Rocky Mountains were born, rising east and north of the Plateau region and providing headwaters for the great Colorado River that, with its tributaries, would carve and chisel the landscape. During this time, the Colorado Plateau began to rise. The end of the Mesozoic Era may have been punctuated with great meteor showers, impacts of many asteroids, and airborne dust that led to the demise of more than half of the species of animals and plants then in existence.
On the Plateau, rock layers range in age from 600 million to a mere 6 million years are still in the horizontal position they were deposited in. Geophysical studies, which measure the thickness of the crust by the velocity of earthquakes waves pass through it, show that the crust is thicker under the Plateau than under surround areas, a factor that contributes to its raftlike integrity and longevity.
Red Canyon: these intricate mazes are sculptured in soft pink rock of the Claron Formation, made up almost entirely of limy Paleocene lake deposits that range from silty and sandy limestone to limy siltstone and sandstone with liberal doses of clay and volcanic ash. The pink color comes from minute amounts of iron oxides, mostly tiny grains of hematite. Red Canyon is pushed up 900 feet higher than Bryce and lie next to basalt dated at 500,000 years old. Paleozoic and Mesozoic layers have been eroded away, and thick layers of Cretaceous marine and near shore sedimentary rocks underlie the Claron Formation. As North American drew away from Europe at the end of Mesozoic time, the continent rose slightly, and the widespread sea in which the rocks were deposited withdrew. In the continental interior rose two ranges that play parts in Red Canyon and Bryce; the Rocky Mountains in Wyoming and Colorado and the Sevier Mountains in Utah. In landlocked basins between the two ranges, large lakes received runoff and finely pulverized rock debris from both. One of these inland lakes stretched diagonally across Utah from northeast to southwest, slightly larger than Lake Erie. In the lake in Paleocene time, silty limestone and mudstone lake deposits accumulated to depths a s great as 1000 feet.
From the ancient gneiss of the Inner Gorge to the white limestone of its rim, Grand Canyon unfolds 2 billion years of Earth history.
500 foot precipice gives its name to the Redwall Limestone, which is really gray but painted with an iron oxide wash from red slopes above.
One of the marvels of Grand Canyon is that it is here at all. Why should a river develop a course directly across a 9000 foot uplift? For the Colorado River bisects the very heart of the Kaibab Uplift, and bisects it so thoroughly that the river flows in desert summer while pine and aspen clothe the cool plateaus above, so thoroughly that animals south of the canyon have evolved differently than those north of the canyon…Regional drainage on the North Rim flows towards the canyon while that on the South Rim flows away from the canyon. The river is 4460 feet below the South Rim and 5940 below the North Rim, and the river is much closer to the South Rim than the North Rim.
In Grand Canyon, Precambrian rocks fall into 3 age groups; the highly metamorphosed Vishnu Schist which had its beginnings more than 2 billion years ago; granite that intruded about 1.75 billion years ago, and a younger group of sedimentary rocks. Studies of the schist show that it was involved in several pulses of mountain building and altered at depths as great as 12 miles below the surface. There was nearly a billion years of erosion in late Precambrian time-the longest, most widespread periods of erosion the Earth has known. Both older and younger rocks were trimmed away to an essentially horizontal peneplain expressed in the Great Unconformity between Precambrian and Paleozoic rocks, not only in Grand Canyon but in many other parts of the world. Recent studies in the Ozarks at the Great Unconformity there may show that the breakup of the ancient continent Rodinia that was uplifted which caused massive erosion.
Research shows that the Cambrian sea advanced in five pulses. Conglomerate and coarse sandstone near the shore, finer sandstone and mudstone further out, and finally limestone where the sea was fairly open. Toward the end of the Cambrian Period, the sea retreated and there is no record of Ordovician or Silurian time here. Either no deposits or it was eroded away. Some found in Ohio show there could have been extensive glaciation on Gondwana which exposed the rock to be eroded away.
The Redwall Limestone was deposited in Mississippian time; thick, strong, and extremely widespread, the limestone contains fossil fish and many small marine shellfish such as brachiopods, corals, mollusks, sea lilies and trilobites. It is bluish gray and stained with red iron oxide mud from the colorful shales above. The top of the Redwall Limestone is marked by erosion similar to that of many limestone areas today, a surface characterized by extremely irregular topography, with many caves, sinkholes and underground channels. This hummocky, irregular karst surface gives us a clue into the Mississippian climates here for such surfaces are known today in Kentucky, Puerto Rico, Slovenia, and other warm, humid climates.
The Supai Group and the Hermit Shale were deposited on a floodplain or delta and in an adjoining shallow sea, some of the rocks bear imprints of fernlike leaves and reptile tracks. A little later in Permian time, windblown sand swept across the Grand Canyon region, leaving a thick deposit of fine white sandstone marked with long, diagonal cross-bedding- the Coconino Sandstone, the white band on the canyon’s upper walls. Tracks and trails of lizardlike animals mark some sloping dune surfaces, but no bones or skeletons of the animals have ever been found. During the rest of Permian time, the western sea continued to fluctuate, twice it inundated the region, depositing the Toroweap Formation and the Kaibab Formation forming 500 feet of the upper canyon walls.
No Mesozoic rocks at Grand Canyon now, but those at Zion, Canyonlands, and Arches show thick layers of sand, mud and volcanic ash were deposited.
Gradual downcutting by the North Fork of the Virgin River shaped the Zion Canyon of today. The North Fork seems to placid to have accomplished all this erosion. But with summer thunderstorms or spring melting of snow on the Markagunt Plateau around its headwaters, the river picks up volume and speed, and pounds its bed with sand, pebbles, and even large boulders, cutting own at an average rate of 1 inch per century, 600 feet per million years. Canyon widening is the job of slides and rockfalls. The Kayenta Formation below the Navajo Sandstone is responsible for most slides; its relatively soft siltstones and mudstones fairly invite erosion.
As the Triassic Period began, this part of North America had just risen above the sea and was lying close to the equator, and formed a broad coastal plain sloping westward toward the ocean. Sluggish rivers wound across the plain, gradually depositing silt, mud and clay derived from the Ancestral Rocky Mountains. In mid Triassic times, the nature and source of the sediments changed. Coarse sands and gravel from highlands in Arizona formed the Shinarump Conglomerate. Still later, fine volcanic ash and mudflows created purple, green and gray layers that contain fossil amphibians and reptiles and make up the Chinle Formation. Coarse river channel and floodplain deposits formed the Moenave and Kayenta formations and indicated cessation of volcanism in late Triassic time. During the Mesozoic Era, North American slowly drifted westward and northeast. By late Triassic time, it had entered the dry subtropical latitudes, then as now the site of major deserts. On a wide, windswept Triassic-Jurassic plain, sand dunes piled up, layer upon layer, for millions of years. This sea of sand, stretching from northern Arizona to southern Wyoming, is now the Navajo Sandstone.
A few layers of red siltstone, the Temple Cap formation and above it are thinner crossbedded sandstone of the Carmel Formation show that the western sea briefly flooded this are near the end of the Jurassic Periods. Much later, in Cretaceous time, the sea advanced again, coming from the east. The Dakota sandstone is the youngest sedimentary unit and in remote areas. Marine sediments- fine gray shales, sandstone, and limestones fill out the Cretaceous sequence in other parts of the Plateau like Arches NP and Bryce Canyon But do not appear in Zion. Near the end of the Mesozoic Era, the Rocky Mountains rose was and norther of here stretching in a great arc from New Mexico to Canada and putting an end to the pulsing incursions of the sea. As the Rockies rose, deep intermountain basins in Utah and Wyoming began to receive rock debris form them. Lakebeds from them show up in Bryce, Cedar Breaks, Red Canyon. All tertiary in Zion have eroded away. Lava flows and cinder cones and evidence of Quaternary lakes with faults deep enough to tap the basalt magma of the Earth’s mantle, dated as 260,000 to 1.4 million years old. The primary geologic process of Quaternary time was and is erosion, the amount of erosion faster in Pleistocene time, when precipitation was greater than at present. About 4000 years ago, a rockslide occurred at the lower end of Zion Canyon, 1 mile above the bridge and junction of the highway routes into Zion. Damming the North Fork of the Virgin River, a long narrow lake existed for 1500 years.
Checkerboard Mesa is capped with striped layers of the Temple Cap and Carmel Formations on Navajo Sandstone, where water has incised small gullies along vertical joints while wind and blowing sand have etched the sweeping cross bedding of this rock.
The highway travels up Pine Creek Canyon and tunnels through Navajo Sandstone at the Kayenta (river and floodplain deposits) -Navajo contact.
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