2. Content
Background & Method
Brief Geological History
River Canyon Geology
Gold Deposits
Rock Examples
Geological Features
Plant Examples
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3. Background and Research Methodology
In late June I visited an area in the canyon of the Middle
Fork of the American River
The photos and rock samples included in this report are
from this field trip
3D map images were prepared using Google Earth
Identification of rocks done using: Geology of the Sierra
Nevada, by Mary Hill (2006)
Identification of plants done using: Trees and shrubs of
California, by Stuart & Sawyer (2001)
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4. Site Location
Near Auburn, California
Entry through Driver’s
Flat Road, on dirt road
down to bottom of river
canyon
Coordinates 38.962362,
-120.929775
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5. Deep Down in the River Canyon
Googl
e
Earth
View up the very deep canyon of Middle Fork of American River
Valley has been carved by the flow of the river for last several million
years
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6. Quick Geological History and Overview
Sierra Nevada is a tilted fault block 400 miles long,
with rugged east face, and sloping west face
West side has metamorphic rock formed by plate
tectonics in Early Paleozoic to Late Jurassic (400-
120 million years ago) – with portions of ancient
seafloor
Volcanic eruptions filled ancient valleys with lava and
mudflows
Present river system formed by erosion during last 5
million years
(Lindstrom, 2000; “North,” 2006; “North,” 2007)
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7. Geology of Middle Fork River Canyon
Undulating steep mountains, elevation 1,600 – 5,600
feet
Foresthill Divide is a NE trending ridge system,
separating North and Middle Forks of American
River
River has cut steep canyons 1000 ft below top of
Foresthill Divide
Significant surface erosion, especially on steep hill
sides
Mean annual precipitation between 30-40 inches
Extremely low seismic activity
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(“North,” 2006; “North,” 2007)
8. Gold Deposits Around Foresthill Area
Streams flowing down western slopes carried
Auriferous gravels
Auriferous gravel <0.5 percent of soil types in the
area
Flows of lava later covered and protected many of
these deposits
Gold veins usually are 3-4 feet thick, in NW direction
Gold discovered in Foresthill in 1850
Primarily placer mines, with extensive hydraulic
mining
In next 15 years more than $10 million was extracted
(“Description,”1897; “Gold,” 1970; “North,” 2006; “North,” 2007)
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9. Rock Sample: Periodotite / Serpentinite
Serpentinite is derived
from basic intrusive rock
It is created through
geological low-
temperature metamorphic
process involving heat in
Description: some small
presence
grains, black/gray color, can be of water
scratched, no layers, can be Peridotite is derived from
fractured the Earth's mantle
Identification: I believe this is
Serpentinite, a plutonic igneous
rock type
(Hill, 2006)
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10. Rock Sample: Greenstone /Green schist
The rock is derived from
basalt, gabbro or similar
rocks containing sodium-
rich plagioclase feldspar,
chlorite, epidote and
quartz
Description: weathered Greenstone and green
red/brown color, fine-grained, schist belts are primarily
can be scratched, faint formed of fine-grained
layering volcanic rocks,
Identification: I believe this is dominated by basalt, with
Greenstone, a metamorphic minor parts sedimentary
rock
(Hill, 2006) rocks
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11. Sandstone Rock Outcropping
Fragile grainy sand-colored
sedimentary rock
Appears to be sandstone or
gritstone
The outer layer, in part, is
held together by a thin layer
of vegetation
Likely result of earlier
deposits of sand, later put
under high pressure from
overlaying sediment or lava
layers
Tilted almost 90 degrees, by
earlier rock folding process
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12. Polished Bedrock Down at River Level
Sections of the rock at
river level has smooth
appearance
Polishing effect likely is
from flowing silt-filled
water
It is difficult to see what the rock type is since the
surface is so changed. It could either be the from
the intruding plutonic rocks, or from the older
sedimentary rocks from older sea bottom
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13. Erosion and Break Up of Larger Rocks
Large boulders cracking and fragment into smaller blocks
Process driven by heating/freezing cycles, as well as
erosion from water, snow, and ice
The large boulder may have come down by rock fall from
higher up in the river canyon as part of ongoing erosion
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14. Tilted Sedimentary Rocks
Appears to be layered sedimentary rock
Could be part of the earlier seabed
Tilted between 60 to 90 degrees, mostly facing NE
Covered by moss and other plants
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15. Plant and Animal Life
Ground around
the river bed is
mostly rocky and
dry
Mixed forest,
oaks, and small
shrubs; with
habitat for diverse
fauna
No major animals
seen, except one
river otter (which
quickly
disappeared
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under the
16. Madrone Tree
• The madrone is a member
of the Heath family
(Ericaceae) of vascular
green plants
• Ericaceae is under the order
Ericales, which evolved from
Magnoliales, which in turn
descended from
I believe this tree is a angiosperms originating in
Pacific Madrone (Arbutus the Mesozoic Era
menziesii) • It has high tolerance to poor
soil, drought, extreme
(Stuart & Sawyer, 2001) temperature, shade, and
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elevation; which enables it to
thrive in many different
17. Evolution of Pacific Madrone (Arbutus
menziesii)
Plantae => Angiosperms => Eudicots => Asterids => Ericales =>
Ericaceae => Arbutus => A. menziesii
Fossilized leaves of a species similar to modern day Pacific Madrone
have been found in northwestern Nevada, the Blue Mountains of
Oregon, and Tuolumne County, CA
This species dates to the Miocene Epoch of 12 to 26 million years ago
The species composition and flora is similar to oak-madrone forests in
California today
Current madrone-related flora is believed to have originated in
southwestern North America
(Axelrod, 1958;Tappeiner & McDonald, n.d.)
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18. Oak Tree
An evergreen oak that is
found in the southwestern
part of North America,
especially in California
Coast Ranges
Often found near creeks
and drainages, growing in
moist cool microhabitats
I believe this tree is a
It is part of order Fagales,
Canyon Live Oak (Quercus
also descendant from
chrysolepis)
angiosperms
May live for up to 300 yrs
(Stuart & Sawyer, 2001)
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19. Evolution of Canyon Live Oak (Quercus
chrysolepis)
Plantae => Angiosperms => Eudicots => Rosids => Fagales =>
Fagaceae => Quercus => Protobalanus => Q. chrysolepis
Early fossil evidence of family Fagaceae found in western
Tennessee, dated to Paleocene/Eocene boundary (Crepet &
Nixon,1989)
Quercus forms swarms of hybrids making precise analysis of lineage
difficult
More than 200 different species of Quercus across every continent of
the world, including 89 in the US, and 20 in California
Quercus in general are wind-pollinated, however, Lithocarpus and
Chrysolepis are insect-pollinated, thus causes major differences in
their flowers
Chrysolepis the most common member of Protobalanus group in
(Crepet & Nixon,1989; Nixon, 2002)
California
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20. Flowering Manzanita Shrub
About 60 species of
Arctostaphylos, ranging
from ground-hugging
arctic, coastal, and
mountain species to
small trees up to 6 m tall
Believed to have come
I believe this shrub is a from subtropical to warm
Mexican Manzanita temperate groups and
(Arctostaphylos pungens) then evolved in response
to the expansion of a
Belong to order Ericales
new adaptive zone: dry
(Axelrod, 1958; Stuart & Sawyer, 2001) climate
20 Also from angiosperms
21. Evolution of Mexican Manzanita
(Arctostaphylos pungens)
Plantae => Angiosperms => Eudicots => Asterids => Ericales =>
Ericaceae => Arctostaphylos => A. pungens
Shares evolutionary history with Pacific Madrone (Arbutus menziesii)
as described on earlier pages
Rich fossil record, and considered to be of Miocene origin, approx 15
million years ago
Radiation of genus occurred 1.5 million years ago during the
Pleistocene
Oldest remains of Arctostaphylos from lower Pliocene Texas
(Adams,1935)
Southern California thought to have been a major Pleistocene center
of distribution and variation, which then shifted northward (Adams,
1935)
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(Adams, 1935; Markos,1995)
23. References
Adams, J. E. (1935). A systematic study of the genus Arctostaphylos. Berkeley Press: Berkeley.
Axelrod, D. (1958). Evolution of the madro-tertiary geoflora. The Botanical Review. 24(7) 433-509.
Crepet, W., Nixon, K. (1989). Earliest megafossil evidence of Fagaceae: phylogenetic and biogeographic implications. American Journal of Botany. 76:
842-855.
Description of the Gold Belt. (1897). pubs.usgs.gov. Retrieved July 7, 2011, from pubs.usgs.gov/gf/041/text.pdf
Gold Districts of California. (1970). Oakland Museum of California. Retrieved July 8, 2011, from http://museumca.org/goldrush/dist-foresthill.html
Hill, M. (2006). Geology of the Sierra Nevada (Rev. ed.). Berkeley: University of California Press.
Lindstrom, S. (2000, July 15). FORESTHILL DIVIDE COMMUNITY PLAN (FDCP) HERITAGE RESOURCE ELEMENT. Appendix B.1. Retrieved July
7, 2011, from http://www.placer.ca.gov/Departments/CommunityDevelopment/Planning/CommPlans/FDCP/~/media/cdr/Planning/CommPlans/
FDCP/RDEIR/Appendices/deir%20rfdcp%20appendix%20b%201.ashx
Nixon, K. (2002). The Oak (Quercus) Biodiversity of California and Adjacent Regions1. US Forest Service. Retrieved July 10, 2011, from
www.fs.fed.us/psw/publications/documents/psw_gtr184/psw_gtr184_001_Nixon.pdf
North Fork American River Trail. (2006, June 1). Welcome to Beautiful Placer County California. The official website.. Retrieved July 8, 2011, from
http://www.placer.ca.gov/Departments/CommunityDevelopment/EnvCoordSvcs/EIR/NorthForkTrail.aspx
North Fork/Middle Fork American River Sediment Study. (2007, April 1). USDA. Retrieved July 7, 2011, from
www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5275882.pdf
Stuart, J. D., & Sawyer, J. O. (2001). Trees and shrubs of California . Berkeley: University of California Press.
Tappeiner, J. C., & McDonald, P. M. (n.d.). Arbutusmenz. Northeastern Area State & Private Forestry - USDA Forest Service. Retrieved July 10, 2011,
from http://www.na.fs.fed.us/pubs/silvics_manual/volume_2/arbutus/menziesii.htm
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