Shutter Ridge in Olema Valley EarthCache
Hidden : 10/3/2007
Difficulty:
3.5 out of 5
Terrain:
2.5 out of 5

Size: Size: other (other)

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Geocache Description:

This unassuming ridge is a shutter ridge on the San Andreas Fault. Shutter ridges are characteristic of transform faults.

The Olema Valley


Olema valley is a typical linear valley indicative of a strike-slip fault (see earthquake trail for what a strike-slip fault is). The San Andreas has fractured the rocks creating a line of easily eroded rock. Water has eroded these fractured rocks, creating the linear valley. At this point, two creeks flow through this valley, one to the north and the other to the south.

From the top of this knoll you can see both creeks. Olema Creek is to the east and flow north and Pine Gulch Creek is to the west and flows south. These creeks actually parallel each other for about 2 miles along the valley floor, but flow in different directions. This ridge separates them. The drainages from hills to the east flow down hill and are diverted north by this ridge. The water flowing down the hills to from the west are diverted south by this ridge.

Because of its effect upon the drainage, this feature is called a shutter ridge. Shutter ridges are elevated pieces of land that are moved in-front of existing drainages by the movement of a strike-slip fault that alter the course of the water flow. Usually the drainages are redirected parallel to the fault line. Shutter ridges can be of any size and do not have to separate two different drainages, just change the course of the flow of water in an existing channel.

By that definition, there is an even larger shutter ridge visible from this vantage point.

Logging requirements:


Please email me through my profile rather than use the message center. Answer the following:

  1. The text "GC16D3H Shutter Ridge in Olema Valley" on the first line
  2. The number of people in your group.
  3. The location and general description of the larger shutter ridge.
  4. The direction(s) that the shutter ridge redirects the drainage(s).
  5. Extra points, Identify the feature west of the secondary coordinates.
Please submit your answers before logging this as a "find." Logs that have not fulfilled the logging requirements will be deleted.

More Information:


There is parking for three or four cars at the trailhead. Follow the well maintained trail even though it may look like it doesn’t go directly to the coordinates. Signs along the trail say that the area becomes flooded after storms and in winter.

Sources

Placement approved by the
Point Reyes National Seashore


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Additional Hints (Decrypt)

Cbvag Erlrf jnf genafcbegrq abegu ol gur Fna Naqernf

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)


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