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Sierra Nevada

Sierra Nevada

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Sierra Nevada

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  1. Sierra Nevada

  2. Sierras • 400 miles long • 50 mile wide • Eastern ridge of the Central Valley • Many peaks above 13,000 ft.

  3. Most of land in National Forest

  4. 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"

  5. 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

  6. 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.

  7. 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

  8. 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.

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

  10. 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

  11. Eastern Slope • Sagebrush Scrub • Desert

  12. 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.

  13. 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.

  14. 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.

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

  16. Biotic Zonation of Sierras

  17. 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

  18. 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

  19. 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

  20. Valley Oaks – 400 ft.

  21. Blue Oak

  22. 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

  23. Buck brush - Ceanothus

  24. Chamise

  25. Yerba Santa

  26. Warm Chaparral

  27. 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,

  28. 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

  29. 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

  30. Grizzly Giant • Mariposa Grove

  31. 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

  32. Upper Valleys

  33. 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.

  34. Geology of Sierras

  35. 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!!.

  36. 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

  37. 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.

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

  39. 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

  40. 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

  41. Postbatholitic rocks • Newest rock formations • Sedimentary • eroded rock debris washed westward, still today. • Volcanic in areas

  42. 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.

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

  44. Hanging Valley

  45. Lava in Old River Bed

  46. V-Shaped Valley