Marin Headlands / Rodeo Beach

Although pre-registration was required, we set up a start table to log people in and stamp books on a beautiful morning for a walk.
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The walk started out zig-zagging up the cliffs and along the hills surrounding Rodeo Lagoon then came back along the beach. It provided spectacular views of historic military sites and the windswept beach, covered with unique red and green pebbles, where you may see (but must not collect) jasper, carnelian, black agate, and jade among the beach sands.

Real quick geology lesson. The Marin Headlands are a fascinating geological formation created when oceanic sediments from the Pacific Plate were scraped off as the plate went under the North American Plate. The primary rocks you find include graywacke sandstone, radiolarian chert, serpentine, pillow basalts, and shale. This beach is unique among California beaches in that it is largely made up of coarse pebbly chert grains, both red and green in color that come from the pillow lava and chert rocks.

Two military forts once guarded these shores. Fort Barry and Fort Cronkhite ó the buildings now serve as National Park Service facilities. Fort Cronkhite is a former US Army post that served as part of the coastal artillery defenses of the San Francisco Bay Area during World War II. The soldiers at Cronkhite manned gun batteries, radar sites, and other fortifications on the high ridges overlooking the fort. The layout of the buildings can be seen from atop the cliffs, and the walk passesd Battery Townsley and a 16" gun of the type that was installed there.

We stopped by and visited the Marine Mammal Center, a private, non-profit organization that was established in 1975 for the purpose of rescuing, rehabilitating, and releasing, marine mammals who are injured, ill, or abandoned.

Fort Barry was part of the Coast Artillery Corps and operated throughout the 20th century, before its closure and eventual transfer to the National Park Service. The balloon hangar at Fort Barry is a surviving element of the U.S. Armyís brief experimentations with using tethered balloons as part of the nationís system of coastal defenses. Constructed and abandoned the same year, the structure is the only surviving hangar of its type that actually housed an army balloon, and one of only two examples of its type known to survive in the country

Rodeo Lagoon empties into the Pacific Ocean when the water level reaches a high enough level to erode through the sand bar. This high water level usually occurs in the winter months. The lagoon is typically oxygen deficit in the summer and fall. This deficit is caused by the high oxygen consumption of decaying algae that occurs during that time of year, causing a real problem for fish survival.

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