The Carson Pass area of the Sierra Nevada range shows evidence of geological changes over millions of years. The underlying granite was formed 150-200 million years ago, and was later covered by volcanic rock. Erosion has exposed multiple layers and remnants of the earlier igneous and volcanic formations. Plant and animal life in the area evolved and diversified as the climate warmed following deglaciation around 10,000 years ago. Conifers and flowering plants now dominate the forests, and mammals such as marmots inhabit the alpine regions.

1. Natural Evolution of the Carson
Pass of the Sierra Nevada
Michael Mosca
Geology 103
Professor Mark Lawler
July 13, 2011

2. The Sierra Nevada Range was formed 150 – 200 million years ago
during the Mesozoic in what is known as the Nevadan Orogeny. It
was formed when magma crystallized within the earths crust
forming igneous plutons.
(Monroe, Wicander 2009)

3. Whats unique about the
Carson Pass area is there
is a transition area right
at the Sierra Crest
between the igneous
Granodiorite rock which
forms the bed surface for
the range and volcanic
Peperite which has
flowed over the granitic
bed (Skilling, Busby
2004) The erosion of this
upper volcanic layer can
be visually examined in
this area.

4. In this slide we can see the approximate 5 to 6 layers of unconformities that
have taken place in the area over millions of years. These show the uplifting
and erosional forces taking place in the area beginning with the uplift and
erosion of the igneous base and the building and erosion of the volcanic cap.

5. This slide shows the igneous granodiorite rock that makes up the
bed surface of the Sierra Nevada. This rock is similar to granite but
contains more minerals. Notice the speckling of the rock, these are
deposits of feldspar and micas within the rock.

6. Here is visual evidence of erosional forces taking place on the
granodiorite surface. This erosion was caused from atmospheric and
glacial forces over millions of years. The boulders sitting atop of the
formation have been placed by glacial plucking ( The glacial ice
pulling the loose rock from the bed surface)
(Pidwirney, Jones 1999-2010)

7. These photos show the upper volcanic layer in the area known as Peperite.
The Peperite was formed when the magma uplifted into the crust layer of
wet sedimentary rock. When rising it plucked pieces of the igneous layers
underneath mixing them with the sedimentary layer. These pieces of
igneous stone mixed with the sediment are called clasts.
(Skilling, Busby 2004)

8. This slide was taken in the Kirkwood area. It
shows the volcanic flow or fluvial moving
downward forming a new uncomformity on the
upper portion of the canyon.

9. This slide shows an area where the erosional
process is beginning to uncover the igneous rock
underlying the volcanic.

10. These are slides of the sierra crest at Carson Pass. The slide on the left is
Elephants Back, it is a solidified lava dome. The photo on the right is
Round Top. Round Top is an ancient volcanic cone that is probably
responsible for most of the volcanic activity in the area.
(Eldorado National Forest Information Site)

11. Evolution of Plant and Animal Species

12. Most plant species evolved from spores in the oceans. The flowering
plants were originally gymnosperms that eventually evolved into
angiosperms or pollinating plants. These pollinating flowers are
dominate in the Sierra Nevada Mtns.. The large forests are comprised of
conifers, mostly pines. These are gymnosperms and are seed bearing. The
seeds are usually in some type of cone until they are spread by air, water,
or animals. (Monroe, Wicander 2009, p.588, p.613)

13. This species of conifer is
named Juniperus
occidentalis. It is native to
the Western United States
and grows in alpine climates
up to 10,000 ft.. It is a
gymnosperm and begins
seed production at 20 years
but has no seed cones until
50 to 70 years. The seeds are
dispersed by animals, water,
and air. The oldest known
living Juniper is 3000 yrs.
Old. (Adams 2004),
(Eddleman, Miller, Miller,
Dyshart 1994 p.131),
Most plant and animal life
increased in this area with
the deglaciation and
warming of the climate
about 10,000 years ago.
(Sierra Nevada Geotourism
2009)

14. This is Spreading Phlox
(Phlox diffusa). It is a
groundflower common to
the Sierra Nevada , it
prefers to grow in rocky
areas. It is in a group of
flowers with ultraviolet
patterns. These are naked
to the human eye but
were developed to guide
insects to the nectar for
pollinization. These are
angiosperms.
(Muir Laws, 2007)

15. This is the Yellow Bellied
Marmot ( Marmota
flaviventris ) also known as
a Rock Chuck. They are
herbivores that also eat
insects and have been
reported to be cannibals at
times (Amitage, Johns,
Andersen 1979, Fraas,
Hoffman 1980).
Marmots evolved from
Therapids during the
Permian Period. These
evolved into placental
animals in the early
Cretaceous Period.
(Monroe, Wicander 2009,
p.624 )

16. References
Monroe, J. S., & Wicander, R. (2009). The Changing Earth (5th ed.). Belmont, CA: Brooks/Cole.
Skilling, I. P., & Busby, C. J. (2004). Retrieved July 15, 2011, from http://www.geol.ucsb.edu/faculty/busby/VSSACFlyer.pdf
Pidwirney, i. (2006). Fundamentals of Physical Geography (2nd ed.). Retrieved July 15, 2011, from
http://www.physicalgeography.net/fundamentals/10at.html
N.p.: n.p., n.d. Web. 15 July 2011. < http://www.enfia.info/natural_history/geology.html>.
Eddleman, L., Miller, P., Miller, R., & Dyshart, P. (1994). Western Juniper Woodlands (p. 131). Retrieved July 15, 2011, from
http://www.fs.fed.us/database/feis/plants/tree/junocc/all.html_BOTANICAL AND ECOLOGICAL cHARACTERISTICS
(2009). Retrieved July 15, 2011, from http://(SierraNevadaGeotourism.org.2009).org/index.php
Laws, J. M. (2007). The Laws Field Guide to the Sierra Nevada (p. 158).
Amitage, K. B., Johns, D., Anderson, D., Fraas, B., & Hoffman, R. (1979). Cannibalism among yellow-bellied marmots. In
Marmota flaviventis (135th ed., pp. 1-8). Baltimore, MD: John Hopkins University Press. Retrieved July 15, 2011, from
http://en.wikipedia.org/wiki/Yellow-bellied-marmot