[2] The islands were donated to the federal government by the Crowley family of San Francisco.

They had been bought by Thomas Crowley at auction in 1926 for $25,000 in the hope that they would become the western terminus of the Richmond–San Rafael Bridge.

East Marin Island, a former vacation retreat, now supports a variety of introduced and native plants and provides critical nesting material and rest sites for the nearby colony.

The submerged tidelands support a variety of resident and migratory water birds such as surf scoter, black oystercatcher, diving ducks, and osprey.

This article incorporates public domain material from websites or documents of the United States Fish and Wildlife Service.