Geology, soils, and the critical zone across 8 field sites
The Sierra Nevada of California supports the world's largest trees — giant sequoias — and some of the most studied geological landscapes on Earth. This field guide explores the geology, soils, and critical zone processes at eight real sequoia grove field sites, from the glacially carved valleys of Kings Canyon to the volcanic ash layers buried beneath Nelder Grove's ancient soils.
Yosemite National Park
Granite domes, exfoliation, biological weathering
Where ancient granite meets living roots
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🌳Sequoia National Park
Sierra batholith, joint sets, weathering cascade
The Sierra batholith up close
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🏔️Kings Canyon National Park
Glacial polish, erratics, moraine dating
Ice age carved this valley
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🪨Kings Canyon National Park
Deep weathering, saprolite, clay formation
Thirty metres of ancient weathered rock
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💧Calaveras Big Trees State Park
Hydraulic mining, sediment transport, landscape recovery
A landscape still healing from gold rush scars
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🌋Sierra National Forest
Volcanic tephra, tephrochronology, soil dating
Volcanic ash buried in the soil
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⛰️Mountain Home Demonstration State Forest
Normal faults, Basin and Range extension, isostatic rebound
Where the earth is pulling apart
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🌿Save the Redwoods League (Private)
Bark beetle, climate-driven dieback, weathering flux
When trees die, the rocks stop weathering
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The critical zone is the thin shell of Earth extending from the top of the forest canopy to the bottom of groundwater — the zone where rock, water, air, and life interact to sustain nearly all terrestrial ecosystems. It is called "critical" because without it, life on land as we know it would be impossible.
Within the critical zone, bedrock is slowly dissolved and physically broken down by water, frost, tree roots, and microorganisms. This weathering releases the mineral nutrients — calcium, potassium, phosphorus, magnesium — that plants need to grow. It creates the pore spaces in soil and rock that store water. It filters and purifies water as it moves from the surface to the water table.
The Sierra Nevada sequoia groves are world-class natural laboratories for studying the critical zone. The groves span a range of elevations, geologies, and climate histories, and the giant sequoias themselves — with root systems that penetrate metres into weathered rock — are major drivers of critical zone processes.