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BLOWING UP BLOSSOM ROCK -
Underwater rocks in Central San Francisco Bay have been a problem since the British Navy sloop "Blossom"encountered Blossom Rock in 1826.
There are four significant underwater rock formations in the San Francisco Bay: Blossom Rock, Arch Rock, Harding Rock and Shag Rock.
Located outside the main shipping channel, near Alcatraz and the Golden Gate Bridge, these rocks have been periodically dynamited since the 1860's to improve the navigability of the bay.
All four are currently between 35 and 49 feet below the low-tide line with pending proposals to reduce them to 50+ feet below the low-tide line.
Blossom Rock, Harding Rock, Arch Rock and Shag Rocks have been modified several times by dynamite.
From 1867 to 1869, Blossom Rock was reduced from approximate elevation of -5' MLLW to -24' MLLW.
At the beginning of the 1900's, Blossom Rock, Arch Rock, and Shag Rocks had their tops removed to a depth below -30' MLLW.
Again in the 30's Arch Rock and Shag Rocks had their tops removed to a depth below -35' MLLW and Blossom Rock was lowered to -40 MLLW.
They still pose a hazard to deep draft shipping as these underwater rock masses extend above -40' elevation referenced to mean lower low water and their are current proposals for more blasting.
Source: San Francisco Maritime and Coastal History Club
