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Rock Fall at Grand Canyon

Taken from Plateau Point
Rock fall at Grand Canyon happens regularly, whether anybody sees it or not.  Yet in the geologic story about how the canyon formed, erosion is the last chapter and explains why the rims are so much wider than the Colorado River at the bottom.
Middle Permian Paleogeography of North America about 275 million years ago – Ancient Landscapes of the Colorado Plateau by Ron Blakey and Wayne Ranney
Over 1,500 million years about one mile of limestone, sandstone and shale sediments were deposited in northern Arizona by oceans, swamps, deltas, beaches and sand dunes.

Ripple marks on limestone
Possibly another mile of deposits on top of that eroded away yet can be seen at Grand Staircase Escalante National Monument, Bryce and Zion National Parks.

Kaibab Plateau
Then about 65 million years ago the area now known as the Colorado Plateau uplifted 6,000-8,000 feet, almost like a cake rising, and left the deposited layers intact.

Taken from Desert View South Rim
Rocky Mountain snow melt forms the headwaters of the Colorado River which are joined by the Green River from Wyoming, San Juan River from Colorado, Little Colorado River and many tributaries to create a fast flowing river full of sediments and boulders capable of carving through the mile of deposits over the last 5-6 million years.

Erosion from the walls of the canyon continues. Because the North Rim is 1,200 feet higher than the South Rim and gets more precipitation, 25 versus 15 inches, water flowing over the rim causes headwater erosion which slowly moves the North Rim further away from the Colorado River.

Fresh rock fall discovered the first week in June
The expansion of freezing water and tree roots also contribute to erosion. Rocks fall regularly but rarely does anyone see it happen. One of my fellow Rangers noticed this fresh rock fall at Grand Canyon one morning from the North Rim Lodge. Damn, we missed it again.
Arizona, Grand Canyon NP , , 9 Comments

Escalante Earth Day

SR89 W Grand Staircase Escalante National Monument UtahWhat better place to spend Earth Day than the Grand Staircase Escalante National Monument, where many amazing discoveries have come from the Earth. SR89 west Grand Staircase Escalante National Monument UtahCreated in 1996 by departing President Bill Clinton and managed by the Bureau of Land Management this Grand Staircase represents 135 million years of Earth history. SR89 west Grand Staircase Escalante National Monument UtahThe diverse geology includes many exposed sedimentary layers on top of the Page sandstone seen near Glen Canyon Dam. Tidal mud, windblown sand, lakes, streams and rivers followed by more sand until 94 million years ago when covered by a shallow sea.
About 145 million years ago towards the end of the Jurassic Period, the climate became more humid. Many dinosaur fossils have been discovered in the Morrison Formation from the period.
The visitor center is small yet provides great displays and knowledgeable people.
The immense size and vast wilderness of Escalante requires many more visits.
Grand Staircase Escalante NM, National Parks and Monuments, Utah , , 16 Comments

Passing through geologic time at Painted Desert Arizona

From ancient ruins at Wupatki through geologic time at Painted Desert.
Old bridge over the Little Colorado River Cameron Arizona
Bridge over Little Colorado River
When you cross the Little Colorado River at Cameron on Highway 89 North you enter the western edge of the Painted Desert. SR 89 N Painted Desert Arizona
Enter The Painted Desert
During the Early Triassic, about 250 million years ago, the mass of all continents known as Pangaea began to drift apart between North America and Africa.
Painted Desert Arizona
The west coast of North America subsided into a flat plain and when sea levels rose these plains were covered with seawater. When the level dropped the exposed land was covered with a deposit of Kaibab limestone. SR 89 N Painted Desert Arizona
Because eastern North America had the highest mountainous land at the time, rivers flowed westward to the low coastal plains. The slow moving waters deposited mostly red mudstone and very fine-grained sandstone. Painted Desert Arizona
At the same time tidal flows deposited gray mudstone and tan limestone. All these layers represent the Moenkopi Formation. SR89 through Painted Desert Arizona
During the Middle Triassic deposition stopped and erosion began possibly due to climate change, a drop in sea level or a slight uplift of the Colorado Plateau region.
Painted Desert Arizona
In the late Triassic, about 215 million years ago, the region again subsided and stream deposits filled valleys and river cuts with sediment of very coarse-grained sandstone and pebble conglomerate known as the Shinarump Member of the Chinle Formation. Painted Desert Arizona
As rivers continued to dominate the landscape mudstones in shades of red, gray, brown, purple, tan, orange and pink were deposited as water flooded over the river banks.
Painted Desert Arizona
In addition, ash from exploding volcanoes fell on the Chinle river plains and eventually decomposed to clay with oxidized iron and manganese that give the rocks more vivid color.
SR89 north Painted Desert Arizona
Echo Cliffs on right
The Painted Desert is referred to by some Native Americans as a “land of sleeping rainbows.” Native American vendors along SR89 Painted Desert Arizona
Native Americans sell arts & crafts along the road
Much of the Painted Desert region is located within the Navajo Nation. The Navajo and the Hopi people have lived in the region for at least one thousand years, however the modern name for the desert comes from the Spaniards who named it “el Desierto Pintado” due to its brightly colored landscape.
Vermilion and Echo Cliffs SR89 N Arizona
Vermilion Cliffs in distance & Echo Cliffs on right
From the flat plain of the Painted Desert I continued up Echo Cliffs towards Page and the Glen Canyon Dam.
Arizona, National Parks and Monuments, Painted Desert , , 8 Comments

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