You should answer as many of the following questions as you can in your write up. Draw sketches in your notebook at every field location of any geologic features. Remember to use a scale. Ask your instructor if you don’t understand what to do.

Overview of trip 2: This trip will focus on coastal processes and hazards, the marine geologic rocks of the coast (Eocene and younger age), large landslides, and evidence of tectonic deformation. Although we will have several major stops with field activities (listed below), we will also stop at various scenic viewpoints to observe geologic features, landforms, natural process, and of course scenery! A pod of Orcas was active close to shore near Ruby Beach during our reconnaissance trip in 2006.


We will leave the Centralia College campus and proceed north on I-5 to Exit 88. We will head east on US-12, following the Chehalis River downstream.

Rest stop: Just after arriving at Aberdeen we will have a short rest and refresh stop. Continue north on US 101 to the Olympic Coast.

Stop 1: Landslide along SR 107: At Montesano, we will take SR 107 south about 3-4 miles to the location of a recent landslide that closed the entire road Here we will observe the features of a major landslide.

Stop 2, Viewpoint and discussion: We will stop briefly at Lake Quinault to check out the view and discuss the geology of the Olympic Mountains and origin of Lake Quinault, which is dammed by a glacial moraine.

Continue north past Kalaloch about 7 miles to Ruby Beach (rest rooms).

Stop 3, Ruby Beach: At Ruby Beach we will walk to the beach and head north to look at geologic features during the low tide.

After leaving Ruby Beach we will go south to Beach 4:

Stop 4. Beach 4: Tides permitting, we will walk north a short distance to Starfish Point to make observations of the geology and beach processes. Upon return we will stop to look at overturned sandstone layers of the Hoh Formation where the beach trail descends to the beach..

Stop 5 Kalaloch: We will stop at the campground and walk to the beach, tide permitting.


Mileages:  5 mi from Exit 82 to 88; 46 mi from I-5 to Aberdeen on US 12 (MP 83.68);   74 mi from Aberdeen to Kalaloch (MP 157.69);   (MP 164.61) Ruby Beach Road


Field trip activities:

En route: Observe the landscape as we drive downstream along the Chehalis River. This valley is the major drainage pathway for meltwaters from the Puget Lobe of the Continental Ice Sheet.

A) Past Oakville, note the exposures of marine sedimentary deposits along the right side of the vehicle. These rocks are estimated to be late Eocene to early Oligocene in age based on fossils. One precise age estimate is 38 Ma (mega-annum).  Fossil crabs are not uncommon in concretions.


B) Why are rocks of marine origin located here?


C) Notice the great width of the Chehalis River valley west of Elma. Can you explain this?

Stop 1. SR 107 landslide: At Montesano, we will take SR 107 south about 3-4 miles to the location of a recent landslide that closed the entire road A) Draw a rough sketch of this landslide. B) What kind of landslide is it? C) Describe the nature of the rock material making up the soil nearby? D) Did geologists make any interpretations about the cause and behavior of the landslide? Landslides are one of the most costly of all geologic hazards!

 Stop 2 Lake Quinault. A) Draw a landscape sketch at this viewpoint.  B) What evidence is there that the Olympic Mountains been uplifted dramatically?  Lake Quinault is dammed by a glacial moraine. A moraine is a deposit of rock and debris produced at the margin or terminus of a glacier. C) What evidence would you expect to find for a moraine? D) What was the source of the glacier, and what caused its growth?


Stop 3 Ruby Beach: A) In your field notes, sketch and label what you see at Ruby Beach.

B) Is there a prominent bedrock bench visible? If so, about how high is it? C) What about the extent of the bench—does the flat top of Destruction Island appear to be an extension of the same bench? If so, what’s the connection?  D) What would cause the erosion of such bench—waves?  Speculate on how that would have happened. E) Is there anywhere that you can see deposits on top of the bench? If so describe. Geologists have interpreted that the top of the bench represents and unconformity. Compare its height here with a similar feature at Beach 4. F) What about the rock composing the stacks here—describe rock types and any sedimentary features you see. G) Is there any consistency from one sea stack or rock outcrop to the next?   H) Examine a sample of beach sand with a magnifying glass and report what you see:  Why is this place called “Ruby Beach”? G) Examine the large cobbles on the beach here and at other stops to see if you can identify a “preferred orientation” or shingling of the clasts. If so, sketch this and show the direction. H) Describe the rock types of the rocks on the beach?




Stop 4 Beach 4:  A) Where the trail meets the beach, check out the bedded sediments and sketch them. These layers have been interpreted as turbidite deposits. Turbidites are the deposits of submarine landslides.

B) Examine the layers up close to see if you tell with way might be up? Any clues? These rocks are part of the Hoh Formation described by Welden Rau. His Bulletin 66, Geology of the Washington Coast between Point Grenville and Hoh River (1973) describes these deposits. This book is on hold in the library, and you can consult it to find out more information. More recently, geologists have obtained a rough estimate on the age of the Hoh sediments of 24 to 16 Ma using “fission-track dating”. They found evidence that the sediments were deposited in water depths of > 2,000m. How did they get here?





Stop 5: Kalaloch: A) Look for the wave-cut bedrock bench at the beach here—where is it?  B) Describe and sketch the sediments exposed in the beach here. C) How would do you interpret the prismatic structures visible in the outcrops? D) Are you observations of the beach cobbles elsewhere similar here? E) Is there any evidence for flow direction of the currents that deposited the coarse material exposed in the beach outcrops? If so, what could be the source?

F) Discuss the possible tsunami hazards here. What are the possible sources of tsunamis?    G) Where you would get information on tsunamis and maps? 



Selected References and web sites

Pazzaglia, Frank J.; Thackray, Glenn D.; Brandon, Mark T.; Wegmann, Karl W.; Gosse, John; McDonald, Eric; Garcia, Antonio F.; Prothero, Don, 2003, Tectonic geomorphology and the record of Quaternary plate boundary deformation in the Olympic Mountains. IN Swanson, Terry W., editor, Western Cordillera and adjacent areas: Geological Society of America Field Guide 4, p. 37-67.

Rau, W. W., 1973, Geology of the Washington coast between Point Grenville and the Hoh River: Washington Division of Geology and Earth Resources Bulletin 66, 58 p.

Rau, W. W., 1977, General geology of the southern Olympic Coast. IN Brown, E. H.; Ellis, R. C., editors, Geological excursions in the Pacific Northwest; Geological Society of America, 1977 annual meeting, Seattle: Western Washington University, p. 63-83.

Rau, W. W., 1980, Washington coastal geology between the Hoh and Quillayute Rivers: Washington Division of Geology and Earth Resources Bulletin 72, 57 p.

Tabor, R. W., 1975, Guide to the geology of Olympic National Park: University of Washington Press, 144 p., 2 plates.

Tabor, R. W.; Cady, W. M., 1978, Geologic map of the Olympic Peninsula, Washington: U.S. Geological Survey Miscellaneous Investigations Series Map I-994, 2 sheets, scale 1:125,000.

Thackray, Glenn David, 1996, Glaciation and neotectonic deformation on the western Olympic Peninsula, Washington: University of Washington Doctor of Philosophy thesis, 139 p., 2 plates.    [a great site based on work of Tabor and others]   Chris Heg’s postings of WA DGER geologic maps   DOT 2006 news release re landslide