Unit 3 3 california geology
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Unit 3.3: California Geology. Geologic Processes:. Tectonic processes inside Earth: Subduction: Pacific plate sinks below North American plate, creates large pools of magma that crystallize – forms batholiths Sierra Nevada Mountain Range

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Geologic processes
Geologic Processes:

  • Tectonic processes inside Earth:

    • Subduction:

      • Pacific plate sinks below North American plate, creates large pools of magma that crystallize – forms batholiths

        • Sierra Nevada Mountain Range

      • Juan de Fuca plate subducts below North American plate, produces volcanoes of Cascade Range

        • Mount Shasta, Mount Lassen

    • Accretion:

      • Slabs of crust “push” into North American plate, form Coast Range


  • Faulting:

    • Uplift and movement of plates creates other ranges:

      • Basin and Range mountains east of Sierras

    • Transform boundary where Pacific plate moves north relative to N. American plate:

      • San Andreas Fault

    • Faulting causes other regions to “drop”, creates basins

      • Central Valley

      • Basin regions of Basin and Range Mtns.

        • Includes Death Valley


  • Surface processes:

    • Water erosion shapes mountains, river valleys.

      • Sierras: rivers cut V-shaped valleys along steep sides

      • Central Valley: along valley floors, rivers spread out and slow down, leaving alluvial deposits

        • alluvium: clay, silt, sand, gravel left by flowing streams in a river valley or delta, typically producing fertile soil

    • Glacial ice carved mountainous regions

      • Creates vast U-shaped valleys as glaciers move

        • Yosemite Valley


  • Deposition of sediment:

    • Desert landforms produced by water, wind

      • Few plants to prevent erosion

      • Ex: dunes and playas of the Mojave Desert

        • playa: flat, dry lake bed where mineral salts form by evaporation

    • Central Valley was once an inland sea

      • As Sierra and Coast ranges uplifted, left Central Valley as a basin, filled with sediment that washed down from nearby mtns.

      • Leaves fertile soil for agriculture


California s natural hazards
California’s Natural Hazards

  • Earthquake Hazards:

    • Tsunamis: undersea earthquakes or landslides can trigger enormous waves.

      • Dozens locally in the past 200 years

      • And from afar: Alaska, Japan

      • Tsunami Warning System alerts coastal communities

    • Seismic shaking: caused by earthquakes

      • Decreases as you move away from epicenter


  • Liquefaction: water-soaked soil becomes thick liquid during an earthquake

    • Can cause building collapse

  • Landslides: loose rock/soil on slopes slides away during an earthquake

    • Steeper slopes = greater chance of landslide

    • More likely after forest fire or droughts because plants that hold soil in place are damaged


Volcano hazards include volcanic ash lava flows and volcanic gases
Volcano Hazards include volcanic ash, lava flows, and volcanic gases

  • Cascade Range volcanoes:

    • Black Butte, Medicine Lake are currently dormant

    • Shasta erupted in 1700’s and Lassen in early 1900’s so are considered active

  • “Volcanic fields”: area covered by volcanic rocks

    • Dormant, but could become active again

    • Long Valley caldera releases CO2 gas that, in high concentrations, is deadly to plants and animals


  • Storm Hazards: volcanic gases

    • Mudflows occur when a mass of very wet soil/rock flows quickly downhill, moves faster as it picks up loose debris

      • More common when rainfall is higher than normal

        • Southern California is more susceptible because it’s a drier region, but can also occur in Northern California

      • Mudflows also occur in regions affected by wildfire

        • Wildfires eliminate the plants that hold the ground in place


California s resources
California’s Resources: volcanic gases

  • Sand/gravel used in construction is mined from alluvial deposits

  • Crushed stone used in cement is limestone from shells, areas once covered by Pacific Ocean

  • Granite, sandstone, shale used for decorative building stone

  • Mineral Resources: includes minerals, rocks, sediments, and products made from them

    • Industrial Minerals: sand, gravel, crushed stone, building stone


Metallic minerals gold silver iron
Metallic Minerals: gold, silver, iron volcanic gases

  • Gold/silver occur in quartz veins in igneous and metamorphic rocks created when mountains form.

  • Placer deposits form when gold/silver settle out of moving water because they are more dense.

    • Gold mined in Sierra Nevada, Klamath, Mojave regions

    • Silver mined in Sierra Nevada

  • Iron found in Mojave Desert: magma heats rock and water producing iron-rich solutions. As solution cools, iron is deposited in rock fractures.


  • Nonmetallic Minerals: volcanic gasesevaporites, clay

    • Borates form when boron-rich water flows into desert lakes and evaporates.

      • Used for making fiberglass, detergents, glass, ceramics, and insulation

    • Gypsum forms when salt-water or sulfur-rich water (in caves and hot springs) evaporates

      • Used in wallboard, plaster, and cement

    • Clay minerals form from weathered feldspar (a mineral)

      • Used in ceramics and for making bricks

  • Gemstones: mineral-rich solutions crystallize deep underground.

    • Tourmaline, garnet, agate, and jade


Major energy resources
Major Energy Resources: volcanic gases

  • Oil: ~15% of US oil produced in California

    • Oil is formed when organic matter (dead plants/animals) sediments, undergoes physical/chemical changes.

    • Shale is “source rock” for this oil.

    • Oil can migrate into nearby porous rocks called “reservoir rocks”


  • Natural Gas volcanic gases: forms along with oil

    • Mostly methane, but other gases as well

    • Less dense than oil, so rises to top of reservoir

  • Geothermal: abundant in volcanic areas

    • A geothermal field occurs where magma close to surface heats ground water (becomes steam).

    • Engineers drill wells that “capture” steam that powers turbines to generate electricity


California s geomorphic provinces
California’s Geomorphic Provinces: volcanic gases

  • Eleven Regions:

    • Klamath Mountains

    • Cascade Range

    • Modoc Plateau

    • Sierra Nevada

    • Coast Range

    • Great Valley

    • Basin and Range

    • Transverse Range

    • Peninsular Ranges

    • Mojave Desert

    • Colorado Desert


  • Klamath Mountains: volcanic gases

    • Considered a northern extension of Sierra Nevada

    • Peaks reach 8,000 feet

    • Gold-bearing gravels

  • Cascade Range:

    • Chain of volcanic cones extending from Washington through Northern California.

    • Mt. Shasta: 14,162 feet

    • Pit River flows through it to Sacramento River


  • Modoc Plateau: volcanic gases

    • Volcanic table land built of lava flows and tuff beds

    • Cut by many N-S faults

    • Bounded by Cascade Range and Basin and Range

  • Sierra Nevada:

    • Tilted fault block 400 miles long

    • Crest culminates in Mt. Whitney – 14,495 feet

    • Gold-bearing veins in Mother Lode

    • Northern boundary disappears under Cascades


  • Coast Range: volcanic gases

    • NW-trending peaks ~4000 feet

    • Northern range separated from Southern range by San Francisco

    • Runs sub-parallel to San Andreas Fault

  • Great Valley:

    • Alluvial plain 50 miles wide and 400 miles long – fertile soil

    • North is Sacramento Valley

    • South is San Joaquin Valley

      • Oil fields in south

    • Sutter Buttes: isolated volcano


  • Basin and Range: volcanic gases

    • Westernmost part of Great Basin

    • Many lakes and playas

    • Includes Death Valley and Owens Valley

  • Transverse Range:

    • “transverse” = cut across

    • E-W trending steep range, instead of N-S

    • Includes San Miguel, Santa Rosa, and Santa Cruz Islands

    • Intense N-S compression causes peaks to rise

    • Petroleum-rich rocks = oil…


  • Peninsular Ranges: volcanic gases

    • NW-trending valleys

    • Topography is similar to Coast Ranges

    • Geology is similar to Sierra Nevada – granitic rock

    • Includes Catalina islands off coast


  • Mojave Desert: volcanic gases

    • Isolated mountain ranges separated by desert plains

    • Fault trends define region: NW-SE and E-W trend that parallels Transverse Range

    • Bounded by San Andreas and Garlock Faults

  • Colorado Desert:

    • Low-lying barren desert basin – 245 feet below sea level

    • Dominated by Salton Sea

    • Depressed block between San Andreas Fault and Mojave Desert




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