Transcript Geology of Joshua Tree National Park Emily Howson, Lindsay

Lindsay Patrick
Emily Howson
Lizz Echard
•Draw a line around the world,
starting mid-center between
Joshua Tree and Death Valley, and
you will touch or come close to
many of the world’s great deserts:
Mojave, Great Basin, Sahara,
Arabian, Iranian, Gobi. Most
deserts occur between the
latitudes of 15 and 40 degrees on
either side of the equator.
• For a first time visitor the
desert only hints at it’s
vitality and may appear
uninviting or bleak; but
surreal geologic features add
to the attraction of this place.
One Of A Kind
• Nearly 800,000 acres
• Southern California
• Is a land shaped by strong winds, sudden torrents of rain, and climatic
extremes.
• Rain Shadow desert
• Junction of 3 ecosystems:
– 2 deserts (mainly determined by elevation), & 1 oasis
– The Colorado Desert (a western
extension of the vast Sonoran Desert)
– “Low”: 3000 ft above
– Eastern & Southern
– Creosote bush, Spidery Ocotillo
& “jumping” Cholla Cactus
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Mojave Desert
“High” (cooler & wetter)
Northern part of park
Joshua Tree (Western part)
•
Lowest absolute elevation & the highest maximum temperature 134°F
• “Basin and Range Province”: A landscape of alternating mt ranges & their
bordering basins
– Explorer John Fremont- “The most repulsive
tree in the vegetable Kingdom”.
• Rain Shadow effect
– Created when mountains lie parallel to moist, coastal areas.
– Oases: Dramatic compared to arid surroundings
Western
4000 feet
– 6 Fan Palm Oases
Water occurs naturally along fault lines
80 to 90 years
75 feet
Shaped like a fan and folded like an accordion
The presence of beetles is actually a sign of a healthy
oasis.
• “As old as the desert may look, it is but a temporary phenomenon in the
incomprehensible time-scale of geology” –Ranger
• plate tectonics, volcanism, mountain-building, & stark erosion.
• 900-5000 ft above
• Sand dunes, dry lakes, flat valleys, rugged mountains, granitic monoliths, and
oases
•
Queen Valley & Lost Horse Valley
•
Pleasant Valley-basins
•
6 Mt ranges
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Little San Bernardino Mountains (southwestern)
Cottonwood
Hexie
Pinto Mountains (center)
Eagle & Coxcomb Mts (eastern)
o Joshua Tree is crisscrossed
with 100’s of faults
o Can see raw rocks &
effects of earthquakes.
o San Andreas Fault on
south side of park (Keys
View)
o Blue Cut Fault (center)
o Fault zones = localized
natural springs
o Pinto Mountain fault
(Maria Oasis-visitor
center) plus 4 other fault
oases
• 100 mil yrs ago, molten liquid, heated by the movement
of Earth’s crust, oozed upward & cooled while still below
the surface.
• granitic rock called monzogranite.
– system of rectangular joints
– 1ST: Horizontal set, removal by erosion of overlying rock, called
gneiss
– 2ND: Vertical set, contact of the monzogranite with its
surrounding rocks
– 3RD: Vertical set, develop rectangular blocks.
• Rock Piles= As ground water filtered down through the monzogranite’s joint
fractures, transform soft clay, the eroded boulders settled one on top of
another.
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Daytime: Birds, lizards, roadrunners, & ground squirrels
Nocturnal: snakes, bighorn sheep, kangaroo rats, coyotes, & blacktailed jack rabbits.
Burrows
Reptiles vs. mammals in storing water
Desert Plants National Park: 700 species
Cryptobiotic crusts- hold the place in place
Wilderness is an area “…where the earth and its
community of life are untrammeled by man,
where man himself is a visitor who does not
remain…”
• Can see the Mexican border/ Mount San
Jacinto/ Los Angeles from the mile-high
Keys View.
• Over 12 million ppl in LA= smog/pollution
Man-made lake 20 miles
outside park, scientists
claimed that it’s messing
with the rain shadow effect.
Admired By Many
• Clear skies & clean air
• Peaceful and tranquil
• An adventure
• Extremely fragile, carelessness may leave
lasting scars or disrupt a system of life that
has existed for eons.
• http://www.nps.gov/jotr/
• http://www.joshua.tree.national-park.com
• http://www.desertusa.com/jtree/jtmai
n.html
• Our Geology book under “Rain
Shadow Deserts”
• Where do oases occur?
• What is the name for the granitic rock
found in the rock piles at the park?
• What famous fault is on the south side of
the park?
• Which of the two deserts (ecosystems) is
considered the “low” desert?
• Why is it a rain shadow desert?