Sierra Nevada

Sierras • 400 miles long

• 50 mile wide

• Eastern ridge of the Central Valley

• Many peaks above 13,000 ft.

• Most of land in National Forest

Climate

• Strong rain shadow – Higher Eastern side ( Nevada) drier

• Biotic Zonation of forest types follows rain and temps.

• West Wetter in Sierra at 5500 ft: –West Slope (Yosemite Valley Floor) 75" – East Slope only 20"

Precipitation: North- South • 300 miles north latitude is roughly

equivalent to 1,000 ft. gain in elevation.– Timberline is 1,000 lower in north than south

• Average annual precipitation at 5000 ft elevation:– Wetter in North- 90 inches– mid: Yosemite – 55 inches– South: Kern County 30 inches

• Maximum Precipitation at 8,000 - 9,000' – less Rain/Snow higher up.

• More than 50% of precipitation falls between January to March – less than 3% in summer

Growing season

• Varies by from 4 to 7 months – Shorter the as you increase in latitude,

elevation.

• Alpine (felfield) has only 4-6 weeks growing season in summer.

• At lower elevations (below snow line) growth is limited by summer drought.– especially on east Slope into desert.

Snow line

• Some snow lower down, but at snow line it accumulates instead of quickly melting.

• Shift from winter growing season (wet) to a summer growing season, at around 3,000 ft.

• Snow releases water slowly. • Snow insulates with trapped air pockets

the vegetation beneath. Above blasted by ice, cold winds

• 10 inches of snow = 1 inch of rain

Precipitation • 8-10 inches of increased rain/snow

per 1,000 ft. gain in elevation at same latitude.

• Some summer thunder showers relieve drought a bit. – But doesn’t add much over-all water

• Much less precipitation below 3,000 because of Rainshadow from Coast Ranges.

Air Temperature

• At night and in winter, typically a drop of 3°- 5° per 1,000 ft. gain in elevation at same latitude.

High Elevations

• Air is drier at higher temps.• Temperatures changes rapidly,

no moderating water vapor.• Wind moves with great speed

over peaks

•Wind shearing, kills / blasts one side of trees.–causes drying, chilling and abrasion to plants/animals.

•More intense uv light radiation•Coarser, drier, more acidic soils

Eastern Slope

• Sagebrush Scrub

• Desert

Summer Thermals • Rising summer thermals over Great Basin

pull air over Sierra.• Air pulled up slope air forms summer

thunder showers (adiabatic cooling).• Causes Chimney effect as winds increase

as they are funneled up upper more narrow canyons. – dangerous for fire conditions.

• Also pull rising air from Great Central Valley, pulls in from coast and get coastal Summer FOG.

• Smog from coast, valley pulled up into Sierras.

• Cooling air (denser air) at night drops back down into valleys in Sierras and into Great Central Valley.

• Created thermal inversion next day until pull releases pressure.

Soil: Edaphic Properties• Edaphic (soil) properties, combined with

slope determine plant communties• Reddish laterite soils very nutrient poor

and may be acidic. – brush and chaparral communities dominate on

laterite soils at lower elevations in foothills.

• Sandstone terraces uplifted from marine bottoms.

• Serpentine soils are difficult for plant roots, many endemic species live here.

Biotic Zonation

• Biotic zonation the General progression, microclimate may allow for over lap between zones for quite a distance

Biotic Zonation of Sierras

Great Central Valley

• Great Central Valley floor - flood plains with rich soil. 0- 400 ft. elevation

• Rain Shadow of Coastal ranges, some areas average 10 inches of rain.

• Soil drains too quickly to support trees, only along water ways (Riparian)

• Grasslands can reach up to 1,000 ft into the foothills

Western Sierra Foothills

• Foothill phases reach up to 1,000 - 3,000 ft. depending on soil, etc.

• On rolling hills and plains, has incredible spring wild flowers and green grasses throughout.

• Valley Oak on Valley floor and riparian corridors

Sierra Foothills continued:

• Blue oak- drier areas, upland. – Deep roots and waxy drought-adapted leaves. – Most palatable of acorns in California

• Interior live oak – – higher elevations, just below coniferous forest

• Foothill (Digger) Pine also found mixed in these areas.– Long 7-13" needles in fassicles of three.– large open cones– round open crowns, multiple trunks

Valley Oaks – 400 ft.

Blue Oak

Sierra Foothills continued:

• North slopes - mixed evergreen forest species:– holly-leaf cherry, buckeye, bay, toyon, interior

live oaks, redbud– scattered Foothill pines or Black oak at higher

elevations

• South slopes: Warm Chaparral – impoverished soils–mostly tough evergreen leaves covered with

resinous oils or waxes not drought deciduous.– Chamise, Ceanothus, Yerba Santa

Buck brush - Ceanothus

Chamise

Yerba Santa

Warm Chaparral

Yellow Pine Zone

• Yellow (Ponderosa and Jeffery) Pines– 1,000 - 6,000 includes Yosemite Valley– Ponderosa dominant along with White fir /

Douglas fir mixed conifer forest. Sugar pine on upper reaches. Giant sequoia locally important, in wetter zones.

• Average of 50 inches rain per year.– Yosemite Valley Floor - 4,000' White fir also

has Douglas fir, and along stream course Red Alder, White alder, Dogwood, Big leaf maple,

Yellow Pine Belt

• Valley floors have beautiful Black Oaks, and Canyon Live Oak along (AKA: maul / gold cup) canyon walls.

• Understory: Manzanita, Gooseberry -currant, berries, Ceanothus. – Also: Mountain Misery and Pinemat

(dwarf ceanothus). – Spice bush, chokecherry, chinquapin

Giant Sequoia• Moister sites in Yellow Pine - White

Fir belt.– north in south sierra– south slope in few north sierra, not

water limited.

• Closed Cone Tree– Importance of fire to reproduction– Other means for cones to open

• We’ll See the Grizzly Giant in mariposa grove

Grizzly Giant

• Mariposa Grove

Upper Zones• Lodgepole Pine - Red Fir belt 6,000 - 8,000.– You see some of these plants at Crane Flat

• Sub-alpine 7,000- 10,000– Great to view over summit to Tuolumne

Meadows

• Timberline- zone above which no trees grows due to limited soils, severe weather.

• Alpine Fell-field 10,000 - 13,000– We saw a recreation of this zone in U C

Botanical Garden

Upper Valleys

Forest helps make their own climate by shading

soil• Shaded soils retain more moisture, more

protected from wind.• Excludes many species from growing

underneath a closed canopy layer.• Shade leaves grow thinner, larger than

leaves grown in full sun.• Light gaps “release” shaded saplings and

they respond rapidly.• Tapered shape of young trees allows

lower leaves to still get light.

Geology of

Sierras

Rocks divided by formation periods:

• Prebatholithic rocks were old sea floor sediments well above newer granitic batholith of the current sierras.– Formed older proto-sierras

• Batholithic rocks formed by magma formation 10 miles below ground by subduction of Pacific Plate under North American, around 160-65 million years ago – 100 million year process!!.

Uplift begins about 80 million years ago

• Pushing up prebatholithic rocks forming Protosierras. – Erosion carried debris westwards as it rose,

creating a flat terrain of rolling hillsides by 40 million years ago.

• Protosierras were probably only a few 1,000 ft in elevation, like today’s foothills.– eastern fossils show no evidence of rainshadow.

• 20-5 million years ago extensive volcanic period in southern Cascades and northern Sierras, with lava flowing over relatively flat terrain

Major Uplifting More Recent:

• 3 MYA major uplifting and tilting on angle– gentle western, steep eastern slope. – Accelerated erosion, removed upper

layers, forms deeper river valleys.– Still continuing, future sierras will be

still higher !!

• uplift in Southern Sierras greater than Northern, higher peaks formed there.

•From: The Geologic Story of Yosemite National Park

•N. King Huber, Ph.D.

Increased precipitation

• erode upper layers, revealing granite rock below.

• leaves a few Roof pendants, the remains of prebatholithic rocks perched on top of granite.– mostly on northern half of Sierras, less

uplifting and erosion.

• metamorphic rocks• fills in central Valley with 10,000-30,000

feet of alluvial debris

Contact zones• Formed between metamorphic and granite

rocks have mineral veins.• At time of intrusion of granitic rocks, heat

from magma drove water towards surface carrying minerals within it, forming veins in fractured overlaying rocks.

• Gold and quartz moved in with hot water, eroded out, as collected in stream, river sediments

• 1849 Gold Rush into Sierras – Panning and later hydro-mining

Postbatholitic rocks

• Newest rock formations

• Sedimentary – eroded rock debris washed westward,

still today.

• Volcanic in areas

Ice Ages in Sierras • Deepen valleys by Glacier action• Rain erosion forms “V” shaped valleys.

– Sierras include watershed from Kern River in the South to Feather Rivers in the North.

• Glacier erosion forms “U” shaped valleys.• Pre-Tahoe and other Glacial periods

– Several earlier glacial periods as far back a 4 million years.

– Cut Yosemite Valley

• Tioga Glaciation- Most recent– Began about 30,000 to 60,000– Peaked 20,000-15,000 years ago– Glaciers in Yosemite only reached to Bridal Veil,

but was 4,000 ft. deep.

Glaciers in Yosemite

• From: The Geologic Story of Yosemite National Park• N. King Huber, Ph.D.

Hanging Valley

Lava in Old River Bed

V-Shaped Valley

U-Shaped Valley

Yosemite Valley Floor

• U Shaped• Convergence

of 2 or more glaciers

• Filled in with alluvium

• Meadows and Forest

Glacial Erosion

• Leaves moraines• Lateral, terminal, medial • Erractics-rocks carried in ice,

dropped and left behind as glacier retreats, out of place

• Hanging Valleys – Side valley cut off by passing glacier below

• Lakes form in tarns• Leave no soil, primary succession.

Erratics on Olmstead Point

Upper Meadows

Re-growth after fire

•

Yosemite Trip

http://mvz.berkeley.edu/Grinnell/2004_Report/

index.html• Uses field report data from between

1914 and 1920

• Compare to now to see effects of development, climate change on Yosemite National Park.

Some changes to the valley floor:

• Altered fire cycle

• Fewer Mountain lions, more deer

How humans, vanishing cougars changed YosemiteDavid Perlman, Chronicle Science Editor

Friday, May 2, 2008