Chapter TwoGeologic History and Processes

Plate Tectonics

• Divergent Boundaryo East Pacific Riseo Salton Trougho Cape Mendocino

• Convergent Boundaryo Cascades: Mt Shasta and Mt

Lasseno Historically: Sierra Nevada,

Coast Ranges, Klamath Mtns.• Transform Boundary

(“Sliding”)o San Andreas

California Through the Ages

• Precambrian Era ends 540 mya• California’s oldest rocks 1.8 billion years

old• Crust under us 1.8 billion years old

oBasin and Range, Transverse Range, and deserts• Many younger intrusions

A nearly 3,000 meter-thick section of Paleozoic-age sedimentary rocks are exposed in the mountain ranges of the eastern Mojave Desert region. This view shows Paleozoic-age rocks exposed on the eastern flank of the Panamint Mountains in Death Valley National Park.

http://geomaps.wr.usgs.gov/socal/geology/geologic_history/index.html

California Through the Ages

• San Gabriel Mountains• Metamorphic and igneous rocks• Complex geologic past

California Through the Ages

• Proterozoic (late precambrian)• A sea covered California• Sediments were deposited

o Later igneous material intrudes

California Through the Ages

• Roof Pendants abundant in Californiao Sierra Nevada’s, Inyo-White Mtns.

Hornfels, cherts, marbles, slates, and quartzites

California Through the Ages

• Northern Californiao More volcanic material mixed with ocean

sedimentso Continental crust crushed together with ocean

crust

California Through the Ages

• Southern Californiao Paleozoic rocks not as commono Some in the Ord Mountains, Eastern

Transverse Range, Peninsular Ranges Some gneiss and schist, Riverside limestone

quarried for cement

http://www.desertmuseum.org/programs/flw_mohave.php

California Through the Ages

• Mesozoic Periodo Lots of subduction

going ono Results in mountain

buildingo Nevadan Orogenyo When the sea began

to disappear

California Through the Ages

• Mesozoic Rocks Importanto Pre-Nevadan

roof pendantso Limestone, slate

• Cenozoic Basinso Filled with

sediments and eroded mesozoic rocks

California Through the Ages

• Mesozoic periodo Granite plutons: Sierra Nevadas

and Cascadeso Franciscan Complex (Coast

Ranges) When sedimentary material was

brought to and crushed against the continent

Chert, serpentine, sandstone, shale

o Klamath Mountains: both plutons and schist from

being pushed against and onto the continental plate

California Through the Ages

• California: 1.8 billion years of rocks• Impressive quantities of valuable minerals,

ores, and other earth resources.• Shaped history and still an import part of the

economy

Gold, Silver, and Other Ores• In and near subduction zones, ocean and continental

crust materials incorporate into magmas.• This magma becomes granitic plutons.• As the magma is pushed towards the surface it comes

in contact with older sedimentary or metamorphic rocks.• As the magma cools, it squeezes into cracks and joints

forming veins.• Often it is the most felsic magma with the most minerals

that forms the veins.• High feldspar veins then cool and crystallize with

precious mineral deposits.

Gold

• Placer Depositso Where veins have eroded into streams, rivers,

lakes, etc.• Mother Lode

o Principal zone of veins of gold or silvero Usually refers to California’s Sierra Nevada .7

mi wide, 120 mile long zone• Hydraulic Placer Mining

o Way of mining with high powered water spray

Mix of Valuable Resources in the North

• Klamathso Chromium, cobalt,

nickel, zinc, copper, gravel, clay, limestone

• Shastao Pyrite, chalcopyrite,

sphalerite, magnetite, mercury

Mines in Transmontane California

• Basin and Rangeo Today: talc, saline

mineralso Cerro Gordo

Silver, lead, zinco Bodie

gold

Mining in the Mojave and Southern Deserts

• Rand Mining Districto Gold, silver,

tungsten, boron• Further South

o Gold, rare earth minerals, iron, limestone, magnetite, hematite, boron