CA -- San Francisco -- Golden Gate NRA (North Side) -- View from...:
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GGNRNV_110729_43.JPG: The Golden Gate
A narrow three-mile channel
Providing a narrow entrance to the west coast's most defensible harbor, the strategic value of the Golden Gate is readily apparent. Between 1776 and 1846, Spanish, then Mexican, guns defended the harbor entrance. Starting in 1846, American soldiers guarded the passage, building fortifications on both sides of the channel, and on Alcatraz and Angel Island.
The Golden Gate is the only major break in the coastline for nearly 1,000 miles. The Sacramento and San Joaquin River systems, consisting of 12 major rivers, drain nearly 40% of California, and all of the water flows our through the Golden Gate. The water is over 300 feet deep in the middle of the channel.
John Fremont, a captain with the U.S. Corps of Topographical Engineers, gave the Golden Gate its name in 1846. "To this gate I gave the name Chrysopytae, or Golden Gate," he wrote nearly a hundred years before the bridge was built.
Completed in 1837, the Golden Gate Bridge is known around the world. Few people know that its name belonged first to the three-mile channel that links the bay and ocean. The first Europeans to see the Golden Gate were Spanish soldiers who discovered it by accident while marching north from Mexico in 1769. They called it "La Boca" (the Mouth) and "La Entrada" (the Entrance). Earlier still, the area's native Miwok called the channel "Mouth of the Sundown Sea".
During the Gold Rush, San Francisco's harbor changed almost overnight from a sleepy frontier anchorage into a vital maritime center. In 1849 alone, 770 ships carried more than 91,000 passengers through the Golden Gate. For the next century San Francisco remained the west coast's major port--during World War II, ships transported 23 million tons of supplies and 1.65 million soldiers through the Golden Gate to Pacific battlefronts.
GGNRNV_110729_46.JPG: Battery Construction No. 129
Last of the big gun emplacements
Never named because it was never finished, this battery was designed for the biggest, most powerful guns ever used by the United States military--16-inch caliber weapons that fired 2,100-pound shells and could hit ships 26 miles out to sea. Construction began in 1942 and was almost complete when it was halted in 1943. World War II had turned in favor of the allies and military leaders were confident that there would be no Japanese attack on this coast.
Though San Francisco's harbor was still the most significant port on the west coast at the close of World War II, coastal defense had changed forever after the aerial attacks on Pearl Harbor. There would be no more big gun batteries--Battery Construction 129 marked the end of seacoast fortifications based on land-mounted artillery positioned to fend off enemy warships.
When work on Battery Construction No. 129 was stopped, the gun barrels had been transported to the site. The weapons were never installed and the barrels lay stored in the tunnel until 1948, when they were cut up for scrap.
Embedded in the walls of the tunnel, you can see the rings through which cables would have been run to maneuver the gun barrels into the emplacements.
To hide the tunnel entrances, and the gun openings, iron rings were embedded into the surrounding concrete to secure camouflage nets. Had the battery been given a name, it would have been placed above the tunnel entrance -- the rectangular inset into the concrete was designed for that purpose.
The two gun positions on the seaward side of this hill were perched 800 feet above sea level, making this the highest coast artillery battery in the country.
GGNRNV_110729_49.JPG: Golden Gate Geology
Deep sea rock high in the headlands
The headlands on both sides of the Golden Gate are composed of ancient oceanic rock pushed to the earth's surface--chert, serpentinite, basalt, and graywacke sandstone. Especially hard and weather-resistant, chert forms the ridgelines.
The rocks you are standing on once resided on the bottom of the Pacific Ocean. The sedimentary rock consists largely of the skeletal remains of minute marine organisms, radiolaria, deposited layer upon layer on the seafloor over the course of millions of years. Scientists believe the radiolarian chert, as the rock is known, and the entire headlands complex, was forced to its present position over millions of years by a collision of the continental and Pacific plates.
Since chert is mostly composed of radiolaria fossils, its layers tell us the origin of these rocks. It takes about 20,000 years for one inch of chert to develop. The radiolaria in these rocks are tropical species from the equatorial Pacific which lived millions of years ago.
As old and enduring as these rocks are, the Golden Gate as you see it today is relatively young. Eighteen thousand years ago the Pacific Coast was more than 25 miles to the west of here, and the headlands towered over a river in a narrow valley. It wasn't until 8,000 years ago that glacial melt and rising sea levels flooded the valley and created the current bay.
Each centimeter of chert contains 10,000 years of sedimentation. The folding and twisting patterns within the layers were caused by the upward thrust and rotation of the rock as the Pacific Plate gradually forced the headlands up out of the sea.
Tectonic journey of Marin Headlands rock:
Studying the fossilized radiolaria within a section of chert, scientists can determine where the rocks were formed. For example, tropical species of radiolaria found in Marin Headlands chert have been traced to the equatorial Pacific.
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