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36 x 38 cm 14.15 x 15 in. Sketch of South Farallon Island Pacific Ocean. The Farallon Lighthouse, the Year It Opened. Twenty-seven miles west of the Golden Gate, the Farallon Islands rise out of the Pacific like broken teeth. Fog, current, and a lack of accurate charts had already claimed vessels; the need for a reliable chart of the approaches was urgent. This is that chart – the first careful U. Survey of South Farallon Island, made in 1855 by Lieutenant William P. Trowbridge of the Army Corps of Engineers, published by the U. Coast Survey under the direction of Alexander Dallas Bache. The Farallon lighthouse was lit that same year. This map and that lighthouse were the federal government’s answer to the same problem. THE MAP IN DETAIL. The sheet combines two kinds of cartographic information that mariners needed. Above, a plan of South Farallon Island drawn to scale, with topographic hachures showing the rugged interior terrain, the Light House plotted on the eastern high ground, and the jagged coastline rendered in careful detail. Soundings and navigational notes accompany the plan. The latitude of the lighthouse is given as 37°41’50N; the longitude is computed twice – from Greenwich in arc, and in time from the 1853 observations – a standard check of geodetic precision that reflects Bache’s exacting scientific standards. Below the plan, three coastal profile views show the island as a navigator would see it from the sea: View No. 1 from direction C-I; View No. 2 from direction A-L; View No. 3 from direction A-B. The jagged, spired profile of the Farallons, with its dramatic peaks and sea stacks, is rendered with real skill by engravers G. 1 shows a small vessel and what appears to be a surveying mast or signal staff on the rocks – likely Trowbridge’s own survey party. Alexander Dallas Bache, great-grandson of Benjamin Franklin, ran the U. Coast Survey from 1843 until 1867 and transformed it into one of the world’s leading scientific institutions. Their collaboration on the Pacific Coast Survey produced the foundational charts of California’s coastline during the most consequential decade in the state’s history. The Farallon Islands had been a site of the sea otter and seal trade for decades before the Gold Rush; by 1855, egg collectors were harvesting murre eggs by the hundreds of thousands to feed San Francisco. The lighthouse that Trowbridge’s survey helped site – perched on the highest point of the eastern island, visible in the plan – stands to this day. From the Annual Report of the Superintendent of the Coast Survey series. 46, chart reference J. Drawn by John G. Rex; engraved by G. Magnetic variation of the needle in 1853: 15°40’E, noted in the lower right data block.

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