The Blasting of Blossom Rock

[Music] on april 23 1870 some 50 000 people from the city of san francisco came to watch a spectacular event as the navigational hazard known as blossom rock was as the carson daily appeal of carson city nevada described it blown to glory the great submarine explosion of 1870 was an astounding engineering feat but it also was symbolic of a city that in just a few decades had grown from a remote backwater to a major metropolitan city called the paris of the west it still teaches us lessons today about the process of urbanization and its effects on the environment it is history that deserves to be remembered frederick william beachy was an officer in the royal navy most notable for his exploration surveying and mapping including detailed surveys of the coasts of ireland and south america in 1825 he commanded a ship that was part of an expedition to map the bering strait it was on that expedition in 1826 that he charted the channel around san francisco bay then a tiny spanish settlement he wrote of san francisco at the time so poorly did the place appear to be people that a sickly column of smoke was the only indication we had of the country being inhabited in the course of his mapping bt discovered a previously unmapped navigational hazard a large underwater rock he wrote it is proper to mention in order to give as much publicity to the circumstances possible that there was discovered a rock between alcatraz and yerba buena islands dangerous to both shipping and boats the hazard would come to be named blossom rock after the ship beachy commanded hms blossom beachy surmised that the rock was large and the hazard could not be removed using existing technology but devised a system whereby sailors could use two notably large redwood trees in the oakland hills as navigational aids to identify the ship's location in relation to blossom rock the marks when honored are the north end of yerba buena island in one with two trees south of palace colorado's too conspicuous to be overlooked the trees located in the area that is now roberts regional recreation area off skyline boulevard in oakland became known as the navigation trees the navigation trees helped steer mariners around the hazard through the period of enormous growth in the san francisco bay area precipitated by the california gold rush in 1848 the population of san francisco was around a thousand a year later after the discovery of gold the population had ballooned to 25 000. the navigation trees may have been more than a thousand years old and quite remarkable a may 2013 edition of sf gate newspaper reports that william gibbons one of the founders of the california academy of sciences later found a stump near where the navigation trees had been that measured 32 feet in diameter not including the bark more massive than any redwood or sequoia that exists in the world today the tree must have been among the most remarkable and gigantic individuals of its species he wrote in 1893 but the old growth redwoods of the bay area fell victim to the growing population sfk quotes stephen edwards director of the original parks botanic garden the redwood forest remained until 1845 when the first lumber mill was built gold and redwood trees soon turned california into the saudi arabia of the 19th century helping it become a state by 1860 all but the one redwood had been chopped down and hauled away by oxen then used to build oakland san francisco and sacramento the deforestation did not spare the trees that beachy called too conspicuous to be overlooked it isn't certain when they were cut down but a different edition of sfgate notes a photograph taken in 1852 from telegraph hill in san francisco still shows the navigation trees but by 1855 the navigation trees had been logged while the loss of the old growth redwoods only a small fraction of the old growth redwoods remain is a tragedy in itself the loss of the navigation trees also deprived mariners now entering a far busier harbor of the tools that have been used for decades to avoid blossom rock the u.s navy tried to mark the rock with buoys but san francisco bay has notoriously strong tide driven currents and tide rips and the buoys were swept away the rock presented a particular hazard as army engineer colonel robert williamson explained this rock was directly in the course vessels are often compelled to take in entering and leaving the harbor was in the track of naval vessels passing to and from san francisco and mayor island navy yard and was also in the way of all passenger steamers and vessels plying between san francisco and the sacramento and san joaquin rivers in 1866 williamson was tasked with the job of removing the hazard a letter from major general richard delafield the chief of engineers gave him the order in addition to your present duties you're assigned to the charge of the following named works survey or examination of san francisco california with a view of removal of blossom rock by blasting this was not going to be an easy feat williamson wrote blossom rock is a sandstone rather hard it's sound aligned with alcatraz and yerba buena islands and about midway between them when the tides are lowest the rock has about five feet of water over it a horizontal section of the rock 18 feet below the surface of the water at mean load tide gives the greatest length of rock at 130 feet by a width of 75 feet to obtain a depth of 18 feet of water at mean low tide would require the removal of a thousand cubic yards of stone removing a thousand cubic yards of sandstone rocks emerged under five feet of water would be a monumental task of engineering williamson and his team conducted a number of blasting experiments over the course of the first three months of 1867 to determine the extent of the effort required and the potential costs the experiments were conducted using casks of gunpowder which had been sealed with tar-covered sail cloth lowered and detonated via insulated wires the engineers conducted tests using 75 125 and 175 pound casks in an effort to determine which size of charge might be most economically effective results were measured by officers of the coast survey who made the soundings before and after the blasts as well as inspected by divers eight tests were done and the results were underwhelming in the eighth experiment the largest 175 pound barrel was used with the result a large volume of water probably 50 feet in height and nearly as much in diameter was thrown up the survey showed that 8.5 cubic yards of stone had been removed in all eight experiments using 12 charges removed a total of just 49 and a half cubic yards of stone the smallest charges tested at 75 pounds produced according to williamson but a little effect based on the tests williamson estimated the cost of removing stone by surface blasting at an astronomical 69.05 cents per cubic yard and the kernel surmised the blasting would become less effective as they blasted towards the top of the rock as there was less water pressure williamson estimated taking the entirety of blossom rock to 18 feet below mean low tide would cost the government more than 138 thousand dollars moreover 18 feet of water at mean low tide was the minimum standard the colonel estimated that taking the stone down to a safer 25 feet below mean low tide would require the removal of another 3 345 cubic yards of stone realizing that surface blasting was going to be too expensive williamson instead suggested building a frame to mount a drill so that charges could be placed more effectively in a drilled hole williamson argued this process would be more economical at least to take the stone to a depth of 18 feet after which surface blasting would be more effective but in 1868 brigadier general barton stone alexander chief engineer to the military division of the pacific offered williamson another suggestion alexander suggested that williamson built a coffer dam an enclosed area on top of the rock that could be drained of water engineers could then tunnel into the rock and strategically place explosives taking off the entire top of the rock in one blast a giant submarine explosion a contract for 75 000 dollars in currency of the united states is the value of and in satisfaction for the said work was issued to alexi w von schmidt a civil engineer who helped build san francisco's first dam and drinking water aqueduct and was a key engineer in the city's cable car system on june 16 1869 the daily ulta california opined the means adopted for the removal was entirely novel in submarine blasting and schmidt undertook the experiment at his own risk his idea for the utter annihilation of the rock when properly put before the public left little doubt that it would prove successful still many doubted that the work could be done the mammoth task took months of preparation first schmidt had to use drills mounted on a scow to even the rock enough to place a cofferdam a crib work of timber was created and floated out to the rock where it was sunk using 200 tons of ballast the crib was anchored with steel pointed piles and the bottom sealed by cement a boiler iron center was then placed inside the crib and the space between the crib and the cylinder sealed with more concrete the water was then pumped from the cylinder creating a dry shaft williams noted that at the cribs top a floor was now laid at a height of 20 feet from the rock and on this a shed was placed containing sleeping and cooking arrangements for about 15 men a shaft was then sunk into the rock williamson explained only one man could work in it at a time the hoisting of the debris was the first done by manual labor as the shaft sunk water would start to seep through the rock schmidt dealt with this by inserting a slightly smaller iron tube inside the first and filling the distance in between with concrete eventually a third even smaller tube had to be placed before a watertight shaft could be sunk deep enough the engineering plan was novel and attracted the interests of the engineering community the newspaper the daily ulta california noted this being the first instance of submarine blasting conducted in this way it has naturally attracted the attention of many miners and engineers some of those men have come from a long distance to visit it and spent a half hour in the submarine subterranean recess by january 1870 the shaft was dug to 30 feet below low water as the shaft went down a steam engine was used to hoist out the debris which was dumped into deep water on the side of the rock from the central shaft workers mostly using picks then excavated the inside of the rock preparing chambers to hold the explosives the excavation was completed on april 20th the excavated rooms were then packed with explosives williamson explained that the explosive was a combination of nitrate and soda which was less expensive than black powder charges using combined 43 000 pounds of explosives were created the san francisco newsletter explained the powder had been placed within the galleries excavated in the rock in kegs and worn out steam boilers of the latter seven were employed each holding 100 to 180 40 pound kegs a powder williamson explained that the kegs were ale barrels that had been sealed with asphaltum all san francisco seemed to come to the key side the morning of april 23 to watch the blast the daily alta california raved it was no doubt a difficult undertaking to perform one that must be watched with the most intense care for one false step or mishap would prove ruinous and destructive and involve the loss many lives colonel von schmidt however undertook the work through his plans and with the gratifying result that it must prove a grand success and in such cases inaugurate a new era in submarine blasting the carson daily appeal wrote 50 000 people witnessed the site there was a wire snag and the original attempt to set off the blast failed to the disappointment of the crowd as the daily appeal continued the crowd all of whom were deadheads began to growl as deadheads always do schmidt had to row along the wire and was finally able to set off the charge at this instant the cry was again raised there she goes and on turning the eyes towards the rock itself a most magnificent scene presented itself the san francisco newsletter wrote a column 300 feet in diameter rose from the bay this column formed the center of another magnificent upheaval of water which surrounded it and extended over a circle of 500 feet the daily appeal noted that some of the pieces of rock were thrown nearly a thousand feet from the blast and one piece of the ladder looked from where this rider sat on telegraph hill to be fully as large as a hogshead after the explosion the daily appeal proclaimed every steamer in sight started its whistle and the bells of the various ships were set ringing the blast was found to have been a great success but the sounding showed that the goal of 25 feet below mean load tide was not quite met because of rubble left after the blast a final engineering feat was required to clear the rubble schmidt devised a rake made of heavy wrought iron weighing two and a half tons and its general appearance was that of an ordinary garden rake except that all of its parts were very much heavier it was eight feet wide each tooth was about 28 inches long and slightly curved with a width of three inches and an average thickness of about five inches the rake was dragged by a scow to drag the debris into the deeper water the great submarine explosion of april 23 1870 was described at the time as the largest submarine explosion on record the spectacular public event was a combination of an astounding feat of engineering that faced unique obstacles and great risks without the loss of a single worker's life in 1903 the army corps of engineers used additional surface blasting to take the level of the rock down to 30 feet below mean low tide and while the buoy still marks the spot today only the very largest commercial vessels are at risk but the success in opening the channel hit another issue as the blasting of blossom and other rocks as well as dredging and disposing of excavated material has drastically changed the underwater environment of the harbor a 2004 report by the u.s geological survey concludes by the late 20th century san francisco bay had become a heavily urbanized estuary perhaps more modified by man's activities than any other major estuary in the united states providing safe navigation channels for commercial vessels of ever deeper drafts while also protecting the biological habitats in the bay will provide critical and complex challenges for the future the effects of urbanization on the environment aren't always easy to see as the u.s geological survey explains the floor of san francisco bay lies beneath its scenic surface and the changes made by man there since the gold rush are not always readily visible that floor represents a record of our past but also a challenge for our future i hope you enjoyed this episode of the history guy short snippets of forgotten history between 10 and 15 minutes long and if you did enjoy please go ahead and click that thumbs up button if you have any questions or comments or suggestions for future episodes please write those in the comment section i will be happy to personally respond be sure to follow the history guy on facebook instagram twitter and check out our merchandise on teespring.com and if you'd like more episodes on forgotten history all you need to do is subscribe you

Channel: The History Guy: History Deserves to Be Remembered

Views: 219,134

Rating: 4.979805 out of 5

Keywords: history, history guy, the history guy, san francisco, california, US history

Id: eJQoe1K9uuU

Length: 16min 46sec (1006 seconds)

Published: Fri Apr 23 2021

Reddit Comments

[u/Positronic_Matrix]

This is exceptional content. The video is so well researched and produced, I was riveted throughout the entire story.

[u/onerinconhill]

They blew quite a few rocks up in the bay