South Beach from Steamboat Point—1866. —Library of Congress
ISLANDS AND ROCKS
San Francisco Bay quickly evolved into a critical shipping port after the discovery of gold. Nearly all of California’s wealth funneled through the Golden Gate. The local, state, and federal governments responded quickly to any hazard to navigation. Blossom Rock became the first shipping hazard identified as requiring a permanent solution and the solution turned into a citywide event.
Islais Bay and Creek prior to filling the wetland. Note the plank walkways used to access boats at both high and low tides. —Photo courtesy of San Francisco History Center, San Francisco Public Library
Blossom Rock lay just five feet below the waterline a half-mile northeast of North Point (near Pier 39). It was part of a four thousand-foot crescent consisting of four underwater rocks starting at Blossom Rock, then continuing to Harding Rock, Shag Rocks, and Arch Rock and terminating at Alcatraz Island. Ideally placed to waylay or even rip the hull from any unwary ship, Blossom Rock was first named and charted as a navigation hazard by Captain Frederick W. Beechey on the HMS Blossom, a British man-of-war visiting San Francisco in 1826. Legend claims the Blossom located the rock by striking it, but there is no documentation confirming that event. Regardless, many a ship has encountered the rock, both before it was charted, and since. An East India ship, the Seringapatam, ran aground on Blossom Rock in the early 1830s, waiting until the tide turned before she could slide off and continue her voyage. Her teakwood hull saved her from serious damage.
The U.S. Army Corps of Engineers began test explosions on Blossom Rock in early 1867 in the hope that it could be topped off to a depth of twenty-four feet. The Corps determined that the approximately 105- by 195-foot underwater peak could be demolished and proposed a budget of $50,000 to accomplish the task.
Alexis W. Von Schmidt, a civil engineer and builder of the first dry dock in San Francisco, proposed using a similar method to remove the underwater impediment as that used for the dry dock. Von Schmidt asked for $75,000 to accomplish the task. The Corps awarded him the contract, to be paid after assurance that twenty-four feet of clearance had been achieved.
Von Schmidt’s team built a square crib at the wharf and then floated it out to the rock. The crib was anchored to the rock and then solid supports were used to fix it rigidly to Blossom Rock. Von Schmidt used the new technology he had devised to build the Hunters Point dry dock, and in October of 1869, he lowered a boiler-iron cylinder nine feet in diameter and thirteen feet tall down to the underwater peak to create a coffer dam, and then sealed it and pumped it dry. His team then inserted a six-foot diameter, seventeen-foot tall pipe inside the first and began the excavation. They excavated downward into the rock to a depth of fourteen and a half feet from the bottom of the dam. From that point, the rock was excavated horizontally to form a cavern sixty feet wide and one hundred forty feet long, with a domed ceiling of twelve feet. Rock columns that had been left for support were replaced with eight-inch by ten-inch wooden beams.
On April 20, 1870, the team began the arrangement of thirty-eight sixty-gallon barrels and seven boiler-iron tanks around the perimeter of the cavern, each one filled with sodium nitrate blasting powder and waterproofed with asphalt. After connecting all with gas pipe and rubber tubing up to the crib on the surface, the underground activity ceased and the cavern flooded with bay water. Von Schmidt announced that the rock would be blown on April 23, 1870.
Blowing up Blossom Rock in San Francisco Bay. —Author’s collection
On that day, thousands of spectators, radiating a holiday spirit, gathered on Telegraph Hill to gain a clear view of the great spectacle. Shortly after two in the afternoon, a boat played out the single insulated wire and anchored eight hundred feet away from the crib. The wire was attached to each of the detonators set to the twenty-one and a half tons of explosives. The salt water of the bay served as the return to complete the connection.
At three-thirty that afternoon, a twist of the crank on the magneto-battery initiated an explosion that sent a column of water and rock shooting upward from two hundred to five hundred feet into the air, depending on who did the reporting. The main black column coming up from the cofferdam was surrounded by shorter columns of debris and water that marked the perimeter of the cavern below. Pieces of rock and timber seemed suspended in air before gradually falling back to the bay. The crowds cheered, and the next day newspapers printed enthusiastic accounts of the event.
Soundings indicated that the results were two feet short of the goal. The Army Corps of Engineers refused payment until Von Schmidt could clear the additional depth. Fashioning a floating platform, with a chain operated rake suspended below, Von Schmidt’s team scraped the remaining fragments off Blossom Rock and finally achieved the required clearance.
Shag Rocks (1 and 2) and Arch Rock were dealt with after Blossom Rock and were reduced to thirty feet below the surface in 1900. In 1903, Blossom Rock was further reduced to match Shag Rocks and Arch Rock at thirty feet. As ships became larger and drew a deeper draft, additional toppings were required. On August 31, 1932, Blossom Rock was lowered again to forty-two feet below the mean level of low water.
Mission Rock, once proudly standing guard over Mission Bay, suffered a different fate. A convenient anchoring point off the bay, it became a dumping place for tons of ballast, which over the years added measurably to its size. Eventually covered with warehouses and a pier, the China Basin fill encroached on Mission Bay, to within a few hundred yards of the rock. At the turn of the twentieth century, the U.S. Navy disputed ownership by the Mission Rock Company. After thirty-eight years of litigation, the U.S. Supreme Court awarded ownership to the Navy. The Navy then decided they didn’t want the island and transferred ownership to Board of State Harbor Commissioners for just under $10,000.
In 1946, plans were made to extend Pier 50 to encompass Mission Rock, creating a super terminal for shipping. The remaining buildings on the island were burned in a massive fire that could be seen from as far as Oakland, and the terminal was built as planned. Mission Rock still exists, but only as a stepping-stone.
Treasure Island remains the exception to the rule. It represents an island built where none existed before. San Francisco wanted to celebrate its two new bridges by hosting the 1939 World Fair but had no suitable land available on which to locate it. The decision made in 1935 to use the San Francisco-Oakland Bay Bridge for access to the fair with a view of the Golden Gate Bridge seemed a natural. The island was to be built on the shoals just north of Yerba Buena Island.
Construction began in early 1936. A series of piles and cofferdams surrounded a four hundred-acre rectangular area. Hydraulic dredging began, but in reverse of the normal method. Instead of removing material, the dredging added it, pumping the bay silt, sand and gravel into the form. The name Treasure Island related to the fill itself, washed down from the gold fields of the Sierra as well as referring to the glitter to be found at the fair. It required twenty-nine million cubic yards of fill dredged from the bay and the Sacramento River Delta as well as fifty thousand cubic yards of loam laid on top after the salt was leached from the fill. Nearly two hundred sixty thousand tons of rock were used to create the containment wall around the island.
By 1938, Treasure Island took shape and before the fill was even dry, the buildings and facilities of the 1939 Golden Gate International Exposition sprouted on the island. A causeway connected Treasure Island to Yerba Buena Island, and in 1939, the fair opened on schedule.
The island was intended to house the San Francisco International Airport after the fair, but World War II intervened. Following the fair, San Francisco traded Treasure Island to the Navy for the land in San Bruno where San Francisco airport now resides. Treasure Island became a naval air base and training center. The year 1993 saw the island