Yosemite NP (1890)
Long history of human occupation: most recent Native Americans
were the Miwok and Mono tribes; Europeans entered the valley in
1851 (predictably chasing after Native Americans). Federal
government gave the land to California in 1864; park was put back
under federal control in 1890; “Buffalo” soldiers patrolled the valley
Geologic History of Yosemite NP
During the Jurassic and Cretaceous periods (200 – 100 my), the Farallon
Plate was subducting beneath the North American plate. Many plutons
were emplaced where the modern Sierra Nevada was to be; the plutons
also contact metamorphosed the existing country rock into hornfels.
As the subduction zone off the California coast became a transform
boundary during the late Cenozoic era (25 – 15 my), the Sierra Nevada
range was uplifted, possibly due to back-arc spreading in eastern
California and Nevada, which created a series of normal faults.
Not only did the Yosemite area uplift, there were some nearby areas that
were volcanic, still (Devil’s Postpile NM).
Weathering creates the famous “domes” of Yosemite; the
process is called “exfoliation” and the rounding of the exposed
rock occurs as cracks (joints) form in the rock where erosion
removes weight from above the rock.
Nevada Falls
(foreground), with
Liberty Dome and
Half Dome behind
Between 15 and 10 million years ago, the newly (re)uplifted Sierra
Nevada streams cut massive gorges, which will then be glaciated.
Valley glaciers, as seen during the Ice Ages at Yosemite NP and
elsewhere, are smaller than continental glaciers. Moreover, valley
glaciers are confined by topography.
There are a lot of words to describe features of valley glaciers.
John Muir, arguably the US’s
first naturalist, created the
Sierra Club in 1872 to spread
the word about nature
conservation. By then, the
state of California already
owned Yosemite Valley but
ranchers and loggers were
trying to claim areas to the
north and south.
President Theodore
Roosevelt and Muir take a
three-day camping trip in
the Sierras in 1903; “the
most influential camping trip
for conservation”.
Hetch Hetchy Valley, north of Yosemite Valley (before reservoir)
Muir’s plan for Yosemite was to allow tourist conveniences like
lodges and concessions in the Merced River valley (Yosemite
Valley) but to leave the Tuolumne River valley (Hetch Hetchy
Valley) as a wilderness. This backfired, as Congress authorized
the damming of the valley in 1913 to supply San Francisco with
drinking water.
In fact, today,
the reservoir is
off-limits, so
no one can
enter the
valley.
Ice Age Floods National Geologic Trail (2011)
The “trail” is a series of disconnected sites spread over hundreds of
miles and four states.
NPS applies ten specific standards to determine national significance.
The Ice Age Floods study region meets four of these standards:
The Floods features are an outstanding example of a particular type of resource. Identified
sites within the Ice Age Floods study area possess extraordinary features that exemplify
catastrophic floods of the Ice Age.
The Floods region possesses exceptional value or quality in illustrating or interpreting the
natural or cultural themes of our nation’s heritage. Existing Floods resources offer an
outstanding opportunity to illustrate and interpret an extraordinary natural phenomenon.
The region offers superlative opportunities for recreation, public use and enjoyment, and/or
scientific study. The proposed Ice Age Floods region ties recreational and visitor use into a
comprehensive and coordinated interpretive program across a four-state area. It also
provides additional opportunities for scientific study by identifying significant Floods
resource areas.
Many features in the Floods region retain a high degree of integrity as true, accurate, and
relatively unspoiled examples of the resource. Because of the immense size and extent of
the Floods region, many features remain that have high degrees of integrity and are
relatively unspoiled.
Geologic setup of the Columbia Plateau
First, erupt a lot of basalt from 17 to 6 million years ago. Whether it’s due to a
hotspot or the subduction zone is not relevant
Then, at the height of the last Ice
Age, bring in a lot of wind-blown
dust from Asia (loess).
Then let the continental glacier grow…
As the Cordilleran Ice Sheet grew, the Purcell Lobe glacier dammed
the Clark Fork River in Montana, creating Glacial Lake Missoula
With enough water impounded behind the dam, the ice itself
will lift (it’s less dense than water) and break up, releasing the
lake’s worth of water
The water will
flow at 65 miles
per hour and
discharge more
water than 13
Amazon Rivers.
Huge cataracts formed, as the loess soil and the Columbia River
Basalt bedrock were stripped away in a matter of hours
Sun Lakes State Park, near Coulee City, WA
Ripple marks nearly forty feet high, spaced a hundred feet apart
(see boat for scale) – West Bar near Quincy, WA
Rhythmites – the silt and clay deposited by every Ice Age flood – are
evidence that the floods occurred dozens of times (Hanford Reach, WA)
Erratics – rocks that were rafted in by icebergs – were deposited
hundreds of miles away, hundreds of feet high on a hillside
Bellevue Erratic, Amity, OR