This document provides a three-phase timeline for the geological construction of Oregon: Phase 1 (Foundation): Rocks from 400-50 million years old formed the foundation, including exotic terranes and batholiths and plutons that served as "mortar". Early sediments formed Oregon's first coast. Phase 2 (Bricks and mortar): Younger volcanic and sedimentary rocks from 60-2 million years covered most of the foundation. Units included the Siletz terrane, an early volcanic arc, coastal sediments and volcanoes. The Columbia River Basalt flood erupted from the Yellowstone hotspot. Phase 3 (Plaster and paint): Rocks from the last 15 million years shaped the

1. Desert Lab(1).PDF
7 6 P a r t O n e / G e o l o g y
Desert Landscapes
Arid (desert) and semiarid (steppe) climates cover
about 30 percent of Earth's land area (Figure 5.2). At
first glance, many desert landscapes with their angular
hills and steep canyon walls may appear to have been
shaped by processes other than those that are respon-
sible for landforms in regions with an abundance of
water. Flowever, as striking as the contrasts rnay be,
running water is still the dominant agent responsible
for most of the erosional work in deserts. Wind ero-
sion, although more significant in dry areas than else-
where, is only of secondary importance.
The distinct effects that running water has on
humid and d.y areas are the result of the same
processes operating under different climatic condi-
tions. Precipitation in the dry climates is minimal,
often sporadic, and frequently comes in the form of
torrential downpours that last only a short time. Con-
sequently, in desert areas flash floods occur, and few
streams or rivers reach the sea because the water often
evaporates and infiltrates into the ground.
Evolution of a Mountainous
Desert Landscape
Mountainous desert landscapes have developed in re-
sponse to a variety of geologic processes. A classic re-
gion for studying the effects of running water in dry

2. areas is the western United States. Throughout much of
this Basin and Range region, which includes southeast-
ern Californta, Nevada, western Utah, southern Ore-
gon, southern Arizona and New Mexico, the erosion of
mountain ranges and subsequent deposition of sedi-
ment in adjoining basins have produced a landscape
characterizedby selueral unique landforms (Figure 5.3).
In a large area of the Basin and Range region of the
western United States fault-block mountains have
formed as large blocks of Earth's crust have been
forced upward (Figure 5.3A). The infrequent and inter-
mittent precipitation in this desert region typically re-
sults in streams that carry their eroded material from
the mountains into interior basins. Alluvial fans and
bajadas often form as streams deposit sediment on the
less steep slopes at the base of the mountains (Figure
5.38). On rare occasions when streams flow across the
alluvial fans, a shallow playa lake may develop near
the center of a basin.
Continuing erosion in the mountains and deposi
tion in the basins may eventually fillthe basin and only
isolated peaks, called inselbergs, surrounded by gently
sloping sediment, remain. As the front of the mountain
is worn blck by erosion, a broad, sloping bedrock sur-
face called a pediment, covered by a thin layer of sedi-
ment, often forms at its base (Figure 5.3C). In the final
stages, even the inselbergs will disappeag and all that
remains is a nearly flat, sediment-covered surface un-
derlain by the erosional remnants of mountains.
Use Figurc 5.2 to answer questions 1 and 2.
1. Where are the desert and steppe regions of North

3. America located?
Desert:
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Figurc 5.3 Stages of landscape evolution in a block-faulted,
mountainous desert such as the Basin and Range region of the
West. A, Early
stage;8. lvliddle stage; C. Late stage.
2. Using an "X" to mark your selection(s), indicate
which of the following statements are commonly
held misconceptions concerning the world's dry
lands.
The world's dry lands are always hot.

7. Desert landscapes are almost complete-
ly covered with sand dunes.
The dry regions of the world encompass
about 30 percent of Earth's land surface.
Dry lands are practically all lifeless.
Figure 5.4 is a portion of the Antelope Peak, Ari-
zorLa, topographic map that illustrates many of the fea-
tures of the mountainous desert landscapes found in
the western United States. Use the map and accompa-
nying stereogram of the area (Figure 5.5) to answer
questions 3-13. You may find the diagrams in Figure 5.3
helpful.
3. On the map, outline the area that is illustrated in
the stereogram.
Use a stereoscope to examine the stereogram,
Figure 5.5.
The vegetation in the area is (dense, sparse), and
there are (few, many) dry stream courses. Circle
your answers.
By examining the map, determine the total relief
of the map area.
Total relief : ft
6. (Continuously flowing, Intermittent) streams
dominate the area shown on the map.Circle your
answer.
On the map, of the two lines, A or B (A, B), fol-

8. lows the steepest slope. Circle your answer.
By drawing arrows on the tn"pr indicate the di-
rections that intermittent streams will flow as
they leave the mountains.
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lake."
L0. Identify the features indicated on the map at the
following letters and briefly describe how each
formed.
Letter C:
Letter D:
The area at letter A on the map is a bedrock surface
covered by a thin layer of sediment.
L1. The feature labeled A is called a(n)

17. E x e r c i s e F i v e / S h a p i n g E a r t h ' s S u r f a c e :
A r i d a n d G r a c i a r L a n d s c a o e s 7 9
( C o u r t e s y o f t h e U . S . G e o l o g i c a l S u r v e y )
12. Bfiefly describe how the Antelope Peak area may
have looked millions of years ago.
L3. Assume that erosion continues in the area with-
out interruption. How might the area look mil-
lions of years from now?
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(fig. 14.17) are of Kame
Springs, California. They are is located west of the Salton Sea
and several dunes are
developed on a generally smooth plain. Carefully examine the
aerial photographs and
compare them with the topographic map.
a. 1ffhat type of sand dunes are developed in this area?

18. b. What is the averege height of the dune crest$ (in feet)?
c. What is the average dune width (in feet)?
d. What is the prevailing wind directiop
e. Does there appear to be any type of vegetative control on the
dune formation?
f. In which direction will the dune migrate? North, South, East
or West?
g. These dunes are actively migrating downwind. Careful
monitoring has shown that
individual dunes have moved about200 meters in a $even year
period. If these
rates of migration continue, about how long will it take for the
dune in the center
of the map (iust south of the 100 ft contour line) to cross the
road to the water
torryer at Clancy?
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239
Lab9.docx
TIMELINE OF EVENTS FOR CONSTRUCTING OREGON
PHASE 1
FOUNDATION — Rocks many miles thick underlie the entire
state and range from 400 million to 50 million years old.
Generalized Geologic Units:
1. Exotic Terranes: foundation blocks of Oregon
2. Batholiths and Plutons: mortar for the foundation
3. Early Sediments: Oregon’s first coast
PHASE 2
BRICKS AND MORTAR — Volcanic and sedimentary rocks
thousands of feet thick cover most of the foundation. These
rocks are generally between 60 million and 2 million years old.
Generalized Geologic Units:

20. 4. Siletz Terrane: last exotic arrival
5. Early Volcanic Arc: Oregon’s tropical volcanoes
6. Coast Range Sediments: 50 million years of mud
7. Coast Range Volcanoes: Oregon’s first hot spot
8. Columbia River Basalt: the Yellowstone hot spot arrives in a
flood of fire
9. Rift Volcanoes: aftermath of the Yellowstone hot spot
PHASE 3
PLASTER AND PAINT — This is the familiar land that we live
on. Rocks hundreds of feet thick began forming 15 million years
ago and continue to be shaped today.
Generalized Geologic Units:
10. Ancient Waterways: home of Oregon's first salmon
11. Rattlesnake Tuff: Oregon’s largest known eruption
12. High Cascade Volcanoes: land of fire and ice
13. High Desert Volcanoes: sleeping giants of eastern Oregon
14. Lakes, Rivers, and Dunes: painting the landscape
15. Pluvial Lakes: Oregon’s inland seas
16. Glacial Deposits: runaway global cooling
17. Ice Age Floods: Oregon's best soils lifted from eastern
Washington
18. Mazama Deposits: a jewel born of destruction
19. Unstable Oregon: land of 10,000 landslides
20. Cascadia Subduction Zone Earthquakes: the big one(s)
1. Which two terranes were the first to accrete to form Oregon?
2. Where did these two terranes form and what evidence do we
have?
3. What geologic processes were predominating during the
Cenozoic?
4. Where did the Columbia River basalts originate and what
land area did they cover?
5. What are some of the geologic regions formed from Oregon
running over the Yellowstone hotspot?
6. What caused the High Lava Plains and Basin and Range

21. Provence?
7. What type of rock erupted from the early High Cascades?
8. What happened in the early Tertiary period in Oregon?
9. What was the cause of the Clarno and Challis volcanic
eruptions?
10. How has Oregon’s climate changed throughout its geologic
history?
11. Describe how Oregon’s climate and geology will change in
the future.
On the accompanying map, clearly mark and label the
approximate location and extent (for instance, a mountain range
is not symbolized by one dot) of the following features and
cities. Use different colored pencils to mark the different
features. Please use blue for rivers, brown for mountains, red
dots for cities, and green for other features.
Rivers and Waterways
1. Columbia River
2. Strait of Juan de Fuca
3. Willamette River
4. Yakima River
5. Puget Sound
6. Skagit River
7. Snake River
Mountains
8. Olympic Mountains
9. Cascade Range
10. Mt. St. Helens
11. Mt. Rainier
12. Mt. Baker
13. Klamath Mountains
14. Willapa Hills
15. Okanogan Highland
16. Wallowa Mountains
17. Oregon Coast Range

22. Other Geographic Features and
Places
18. Columbia Plateau
19. The Palouse Hills
20. San Juan Islands
21. Vancouver Island
22. Grand Coulee (not just the dam)
23. Crater Lake
24. Snake River Plain
25. Glacier National Park
26. North Cascades National Park
27. Gray’s Harbor
28. Newberry Volcano
29. Methow Valley
30. Hell’s Canyon
Cities (WA, unless otherwise stated)
A. Seattle
B. Portland, OR
C. Yakima
D. Spokane
E. Olympia
F. Bellingham
G. Wenatchee
H. Richland/Pasco/Kennewick (Tri-Cities)
I. Tacoma
J. Orting
K. Forks
L. Republic
M. Boise, ID
N. Missoula, MT
O. Eugene, OR
P. Salem, OR
Q. John Day, OR
R. Joseph, OR
S. Cache Creek, BC
T. Vancouver, BC