Geology 101, Spring 2008
Writing field trip
modules
One of the best ways to study geology is to go to the place where the earth materials and processes you want to study exist in the environment. From this trip, you will choose a topic on which to write a report for a middle school teacher who wants to take students into the field. Assume that the teacher has a background (one or two college courses) in geology.
The topics are (choose one):
¥ Meet the Three Rock Types
How do you distinguish between the three rock types? What characteristics do they have? Where are they found?
¥ Older/Younger: The Principles of Relative Dating
What is Òrelative datingÓ? What are some basic principles of relative dating? How are these principles demonstrated in nature?
¥ CSI: Central Washington – Evidence for Plate Tectonics
What kinds of plate tectonic interactions are there? How do roadside outcrops illustrate different types of interactions, especially when the tectonics happened such a long time ago?
For your topic, you will write a module for the teacher. A module is a self-contained lesson plan that the teacher can use Òoff-the-shelfÓ with minimal preparation.
Thus, each module should have:
- one or two pages of introduction, giving college-level background material (including any technical terms that need to be defined).
- the pre-trip preparation for the students: what does the teacher need to introduce to the students so that they will understand what they see on the trip. Notice that this is not the same as the introduction for the teacher.
- the description of the trip, which should include directions on how to get to each stop (GPS coordinates good), what is to be seen at each stop (mention colors, features, etc.), and some questions that the teacher might anticipate the students to ask (give answers too!). You must use at least three stops from this trip. Photos are helpful but not required for this part.
- the post-trip activity for the students: the day after the trip, what could the students do in a classroom to fully incorporate the trip topic into their brains? Include a list of materials and equipment that the teacher might need to gather together.
The module should be word-processed, double-spaced and proofread. Do not attach this handout. The Loft (second floor of the library) is an excellent proofreading resource for you. The module is due Friday, October 24 at 4 p.m. You may either turn in a hard-copy or send an electronic file to tfurutan@northseattle.edu (make sure your subject line mentions ÒGeology 101 field tripÓ).
Take I-90 east to exit 70 (Lake Easton State Park). Follow the signs to the park, park the vehicles and walk to the shores of the lake.
Stop 0: Darrington Phyllite
(Cretaceous Period)
GPS coordinates:
Examine the rock
outcrop by the shore. What type of rock is this (its name is phyllite, but
thatÕs not the type of rock it is!)?
How can you tell what
type of rock it is?
What does the rock
type imply about the conditions under which the rock was crystallized?
Return to I-90 and continue east to exit 80 (Roslyn-Salmon La Sac). Turn left under the highway and continue for about 4.5 miles and make a left onto State Route 903 towards Roslyn and Salmon La Sac. Follow the road about 12 miles and pull off to the left (along the lake) and examine the outcrops on the right.
Stop 1: Swauk Formation/Teanaway
Formation (52 to 47 my)
GPS coordinates:
Sketch the outcrop and identify and label the whitish rock. Include a scale!
Identify and label on the sketch the black rock surrounding it. What type of rock is it? How did this rock get here?
What is the age relationship between the white rock and the black rock? What relative dating principle is invoked here?
Is the white rock altered by the presence of the black rock (look at the white rock at stop 2, then look at the white rock near the contact)? So what type of rock is the white rock, technically?
From the white rock, derive a rough paleocurrent (compass) direction of the black rock.
Turn around and drive 1.7 miles, pulling off into a
turnout on the right. The outcrop is across the road.
Stop 2: Swauk Formation (55
– 51 my)
GPS coordinates:
How do the Swauk Formation rocks here differ from the Swauk Formation rocks in the previous stop? What is the rock type and name?
Identify the clasts visible in the outcrop. Identify the fossils, if any, in the outcrop.
Have the rocks of the Swauk Formation been tectonically affected since they were deposited? If so, sketch evidence of this deformation.
As you drive back down the road toward I-90, look at the overlying Teanaway Formation. Has it been tilted like the Swauk Formation? What kind of contact (conformable or unconformable) exists between the Teanaway and Swauk Formations?
Return to Cle Elum and continue on SR 970 through town. At the intersection with SR 10, take SR 10 along the Yakima River. After about 5 miles, pull off the road at a turnout; the outcrop will be across the road.
Stop 3: Manastash Ridge Member of
the Ellensburg Formation (17 - 16 my)
These rocks represent fluvial (river) and lahar (volcanic mudflow) deposits.
GPS coordinates:
What type of rock is this? What are the names of these rocks? Hint: itÕs at least two different rock names (as indicated by the sources listed above). Sketch part of the outcrop that has these two rocks and label the sketch with the rock names. Note that the grain size of these rocks will be key in identifying the rocks.
What was the source of the sediment in these deposits? In other words, from what geographical feature did the sediment originate? Hint: identify the bigger clasts!
Does the variation in grain size between the rocks tell you anything about the energy of the transport agent that brought the sediment here? In other words, was there a variation in the stream (or whatever) flow rate?
Are there any faults in this outcrop? Sketch an example (you may have to walk up or down the road to find one). Are these faults younger or older than the rocks? What dating principle is illustrated here? As usual, include a scale.
What kind of tectonic stress did these rocks experience (hint: you can tell from what type of faults these are)?
Besides the faulting, what evidence is there for the type of deformation seen in the Swauk Formation (a much older formation)?
Continue east on SR 10 for several miles, until you see
some yellow in the rocks on the roadcut to the left. Pull over at a convenient
turnout overlooking the Yakima River.
Stop 4: Grande Ronde Formation
(17 my)
GPS coordinates:
What is the type and name of the dark rock here?
The dark rock forms shapes. Sketch part of the outcrop, showing some of the structures that will allow you to answer the questions below. Include a scale.
The yellow-brown material is the glass palagonite, which is a mixture of clay and iron oxides formed when the dark rock reacts with water. Even though you canÕt see it, what kind of material would you expect underlies the basalt? What was the environment like in this area before the dark rock flowed into it?
Continue east on SR 10. Turn left on Hayward Road, continue for a few miles then turn left on Bettas Road, which will eventually join US 97. Follow US 97 north for about 12 miles, where there should be a quarry north of the road. Park and examine the quarry walls; be careful of falling rocks!
GPS coordinates:
Is there only one type of rock exposed here? Sketch the outcrop, showing any stratification. DonÕt forget to give a scale and orientation.
What is (are) the type(s) and name(s) of the rock(s)? Label your drawing with these names.
What was the origin of these rocks? In fact, due to this, Tabor et al. were able to obtain a fission-track age on zircons in this outcrop of 48.4 ± 2.3 My and 50.5 ± 1.2 Ma.
Is there evidence that these sediments have been reworked (in other words, resuspended in a transport fluid and redeposited)? If so, what is the evidence and to what extent were they reworked?
There has been much debate over the age of these rocks. Tabor et al. used the zircon ages above to infer that the Silver Pass rocks are an interbed of (in other words, contained within) the Swauk Formation rocks. Cheney argues (and I agree) that the zircon mineral grains were chronologically reset by the Silver Pass volcanic deposits and that the Silver Pass volcanic rocks unconformably overlie (and therefore are younger than) the Swauk Formation.
Continue north on US 97 for 2.1 miles and pull off to the south (right) side of the road opposite some obvious outcrops. Be careful crossing the road.
GPS coordinates:
How is the Swauk Formation rock here different from the rock of the same formation in stop 2?
Do any of the units contain any fossils? If so, sketch them in the proper place, and note what organisms are represented.
Now, using all the information above, infer the probable depositional environment.
What can you infer about the paleoclimate of this area?
Resume heading north on US 97 for 7.0 miles to an prominent outcrop on the right with a large dark vertical stripe in the rocks. Pull off the road on the south (left) side and examine the outcrop on the south side first.
GPS coordinates:
Sketch the outcrop, showing contacts where there are distinct changes in grain size. Do not correct the dip in the rocks (in other words, donÕt flatten the layers out). Remember scale and orientation! Label your sketch with the proper rock names; there should be more rock names than at the previous stop.
Cross the road carefully to examine the dark vertical stripe. What rock is it? What type of feature is this? To confirm this suspicion, look at the host rock (the rock surrounding it) on either side. What has happened to the host rock, presumably due to the darker rock?
Should the vertical stripe rock be older or younger than the host rock? In fact, Tabor et al. have dated this rock at about 47 My.
Resume heading north on US 97 for 5.5 miles to Forest Service Road 2322 (Ruby Creek Road). Park on the east (right) side of US 97 and begin by crossing the highway (be very careful) and examining the rocks on the outcrop on the west side of the road.
GPS coordinates:
What rock types (igneous, sedimentary or metamorphic) do you see? These are rocks of the Ingalls Tectonic Complex, which is part of an ophiolite sequence. An ophiolite is a preserved part of ocean lithosphere found on land.
What is (are) the rock name(s)?
Recross the highway and walk up Ruby Creek Road for a few hundred yards. Stop periodically to examine the rocks in the outcrops.
What rock types (igneous, sedimentary or metamorphic) do you see?
Where possible, identify the rock names. You should be able to see some serpentinite, which is a shiny rock fashioned when hot water alters the chemical composition of basalt. What type of rock is this?
From these observations, is the Ingalls Complex deformed or relatively undisturbed by post-deposition tectonics? As you go further east on the road, note what happens to the appearance of the rocks. Specifically, slickensides should begin to appear, causing the shiny rocks to be even more smooth-looking and reflective. Why do you suppose this phenomenon occurs here?
At some point on your eastward walk, the rocks should appear radically different. Identify the rock type and name. What formation do you see here?
Go back to where the change seems to have taken place. Is there a line which separates the two different rocks? If so (or can infer there should be one), this is the fault. The trend of a fault is the compass direction in which it seems to be oriented. What is the trend of this fault? Would you characterize the fault as steeply-dipping or shallowly-dipping?
Return south on US-97; turn right at SR 970 into Cle Elum, where you can get on I-90 westbound.
Alternate
stops
Starting from stop 4: Continue east on SR 10. Turn right onto Hayward Rd. (aka Thorp Highway). Turn right again at Taneum Road and continue until you cross I-90 (the road will now be called Taneum Canyon Road). Reset the trip meter. At 2.7 miles, pull off to the right, on the shoulder of the gravel road at the base of some large cliffs.
Stop 5a: Grande Ronde Formation and
an unknown member of the Ellensburg Formation (20 - 15 my)
Continue on Taneum Canyon
Road (Forest Road 33) to 5.7 miles. Pull off to the right.
Stop 6a: Manashtash Formation (50 my) — Note the
name (and age) is different from Stop 3Õs formation!
Continue on FR 33 (follow signs to Cle Elum). At 8.9 miles, stop at the inter-section of FR 33 and FR 133. Walk about 100 feet up the right fork in the road.
Stop 7a: Cascade Basement Rocks (Jurassic/Cretaceous)
