Not a Mere Overlook EarthCache
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Muir Beach Overlook provides a beautiful place to look out over the rugged coast. It is identified by a small sign on Highway One, north of Muir Beach.
The Overlook provides an opportunity to think about the movement of land over time and the forces of the ocean that pounded the bluffs to form the landscape we see today. Unlike "traditional" caches, there is no container here with a log for you to sign. The earth itself is the cache, and what you learn here about the geology of the area will allow you to answer the questions below and log this earthcache as a "find."
Sea Stacks and Faults
Sea stacks are the most prominent geological feature in the area and give the coast line its striking, picturesque look. They are formed through processes of coastal geomorphology, by the forces of water, wind, and time. Sea stacks develop when the ocean opens up small cracks in a headland and erodes the softer rock. The more resistant rock is left as pillars or stumps, rising from the water and the coastal shore.
The stacks here are part of the Franciscan Complex, which resulted from the collision of the North American Plate and the plate under the Pacific Ocean. During this collision, the rocks were crushed into melange, a mixture of lava and ancient deposits from the sea bed. As the soft portions of the rocks eroded, the resistant rocks endured.
The movement along the North American and Pacific Plate boundary also shaped the area and continues to affect the geology of the area. The San Andreas Fault lies just offshore. All land west of the fault is on the Pacific Plate, moving slowly to the northwest, while the land east of the fault is moving southwest under the influence of plate tectonics. Because each plate cannot move freely, tremendous pressure builds up. When this pressure becomes too great, the underlying rock breaks loose and the surface moves. This is what happened in the 1906 quake that devastated San Francisco and dramatically moved the Point Reyes peninsula.
You can learn more about sea stacks and the movement of the earth by reading the informational signs at the posted coordinates.
Logging Requirements
To log this earthcache please identify the name of the cache and answer the following questions in a separate email to the cache owner:
- What are the names of the two primary rocks that form the sea stacks in this area?
- If you look to the North you will see Point Reyes (on a clear day) and the Bolinas Peninsula. What plate do they sit on? Is the Point moving towards you, away from you, or at the same rate as the land where you are standing?
- How far do you estimate that the sea stacks extend into the ocean? What does this tell you about how the area has changed over time?
- Try to imagine this area far into the future. What geological changes would you expect to see over the course of several millennia and what would be the cause of these changes?
- Post a photo of the Overlook view with your log that includes you, your gpsr, a personal item or informational signs (that do not show any answer). Please note that June 2019 guidelines allow photos as a logging requirement.
Please submit your answers before logging this as a "find." Logs that have not fulfilled the logging requirements will be deleted.
Additional Information
The Muir Beach Overlook is an excellent place to view migrating gray whales between November and June. This site also contains several historic base-end stations. From these stations, soldiers were able to measure the distance, speed, and direction of ships based on angles from different locations. They were particularly important after the bombing of Pearl Harbor in World War II, during a time when people feared an invasion. The use of radar rendered the stations obsolete.
There is a short trail that follows the narrow crest of a coastal promontory to the Overlook. On either side of the promontory, the land sheers off dramatically down to the ocean hundreds of feet below. The cliffs can be dangerous. Please stay on the trail and do not climb over the rails.
The Owl Trail also offers great views of the coastal area and can be a particularly fun family adventure. It starts from the north end of the Overlook and parallels Highway One all the way to Slide Ranch (a two mile round trip). If you are lucky, you may see one of the trail's namesakes, a great horned owl, perched in a tree along the way. Slide Ranch is a working ranch that is open to the public, with an assortment of farm animals. You can continue from there down to North Beach, a secluded rocky area with great tide pools. A handrail and rope will help you down to the beach so that you can see the Stacks up close, but take care if the ocean is rough.
The National Park Service maintains this area and their assistance in developing this earthcache was invaluable. There is much to explore in the area, including Muir Beach and Muir Woods. Enjoy your visit!
Additional Hints
(No hints available.)