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Western Coastal & Marine Geology

U.S. Geological Survey
Open-File Report 98-139
Version 1.0

Multibeam Data and Socio-Economic Issues in West-Central San Francisco Bay

Rock Pinnacles, II

Harding Rock, Shag Rock, and Arch Rock are three bedrock pinnacles in west-central San Francisco Bay that may pose a hazard to navigation. These figures illustrate a scenario whereby Harding Rock might be graded to a safer level.

Pinnacles and depressions on the SF Bay floor

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Three rock pinnacles--Harding, Shag, and Arch on the floor of west-central San Francisco Bay--lie adjacent to the navigation lanes and rise to potentially hazardous elevations for shipping traffic. The shallowest parts are outlined in yellow. Nearby depressions are outlined in orange.

 Profile View of Harding Rock in SFBay
Hypothetical Remedy for a Threat to Navigation

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This is a cross-section through Harding Rock and an adjacent depression. The volume calculations show that the graded material would fit in the adjacent hole. This is merely a geometric exercise and no such solution or option should be undertaken without extensive studies of environmental and other impacts.
Harding Rock and adjacent depression on the SF Bay floor

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The peak of Harding Rock is 36 feet (11 meters) below sea level. The vertical exaggeration is 10x. The gray mesh is 150 x 150 feet (46 meters).

 Harding Rock graded, and material deposited in adjacent depression

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This is a view of Harding Rock if it were graded to 55 feet (17 meters). The vertical exaggeration is 10x. The gray mesh is 150 x 150 feet (46 x 46 meters).

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