Simms Island is a former marsh island in San Francisco Bay. It is in Marin County, California; Its coordinates are 37°57′33″N 122°30′18″W / 37.95917°N 122.50500°W / 37.95917; -122.50500 (Simms Island), and the United States Geological Survey (USGS) gave its elevation as 13 ft (4.0 m) in 1981. It appears as an island on a USGS map in 1897; it is labeled in a 1954 map, but fully connected to the mainland.

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  USGS survey map from 1897.
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  USGS survey map from 1954.
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  USGS aerial imagery from 2021.