Willow Lake Rocks EarthCache

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CacheDFish: It's time

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Hidden : 11/5/2014
Difficulty:
2.5 out of 5
Terrain:
2 out of 5

Size: Size: other (other)

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Geocache Description:


Willow Lake and Granite Lake are located just West of Four Lakes, WA and are thought to be two of many area lakes developed during the Missoula flooding at the end of the last ice age. While these lakes are popular for water sports from boating as kayaking or sailing, they are rather shallow (2'-15') they are also full of algae and in Willow Lake there is a lot of iron in the water.

For this earthcache you will be observing the rock at the shoreline of Willow Lake, at the listed coordinates. In observation of these two lakes we find a different rock formations present at the shoreline and at higher elevations. Finally you will make a hypothesis on the types of rocks that are present at this location and why.

To get started lets take a brief lesson in geological vocabulary and identification of one variety of rocks.

Foliation: Foliation is layering of different types of rocks under conditions of extreme pressure or temperature. The layers form parallel to the direction of the shear, or perpendicular to the direction of higher pressure. Foliated rocks are grouped into the subcategories in increasing metamorphism as Slate, Phyllite, Schist and Gneiss based on grain size and foliation type.


Slate:Slate is a fine-grained, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism

Phyllite: fine-grained metamorphic rock formed by the reconstitution of fine-grained, parent sedimentary rocks, such as mudstones or shales.

Schist: Schist is a foliated rock with a strong habit of splitting into layers. Distinct banding is typically not present in schist, which is typically due to pressure applying to the layers of rocks from multiple directions.

Gneiss: Gneiss is a foliated rock with distinct banding. It tends to be a medium or coarse grained rock, and usually follows a pattern of dark/light alternating bands. The distinct bands typically are a result of pressure applied mostly from one angle or direction.

Identifying rocks through their physical attributes can be achieved with minimal examination by observation and feel. Is the rock layered, smooth, rough?


In highly foliated rocks you will notice more layering and banding is present than less foliated rock.


Logging Requirements: After you have physically visited the site please email me the answers to these questions at the same time as logging your find. Reference "Willow Lake Rocks" on the first line. Do not post answers in your log.
1-From what cardinal direction(s) do you believe pressure was applied to form the layering in the rocks present at this location? Why do you believe so?
2-What classification(s) of rock do you see present here? Why do you believe so?
3-What kind of rock is prevalent in this region, but not present on the shore line. Why do you believe this is true?

Additional Hints (No hints available.)



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