Long before the Navy arrived, Skaggs Island was tidal marsh -- part of the vast wetland system fringing San Pablo Bay and a critical stop on the Pacific Flyway for migratory birds. Native Americans used the area extensively until the 1800s, when federal legislation gave California permission to fill in wetlands for development. Senator John P. Jones of Nevada purchased 10,000 acres and sent his brother to develop them. Chinese laborers, many of them freed from railroad construction work, built the levees that controlled flooding from Sonoma Creek. The island that emerged from their labor became diked farmland -- hay fields and salt ponds stretching across a landscape that had once been water. The name came later, from Marion Barton Skaggs, a grocer turned benefactor who bailed out the struggling Sonoma Land Company during the Depression of the 1930s.

The Navy purchased the site in 1941, recognizing what geography had always made obvious: a flat, isolated marsh surrounded by water was ideal terrain for radio antennas. By 1942, Skaggs Island was operational, and for the next five decades it served as a hub for communications and intelligence gathering -- not just for the Navy, but for other federal intelligence organizations whose involvement remains only partially documented. The base housed an AN/FRD-10 high-frequency direction-finding system, a Cold War-era array designed to locate radio transmitters by triangulating their signals. Self-contained and heavily secured, Skaggs Island was the kind of facility that appeared on maps but never in newspapers. The sailors stationed there joked that they could not tell their families what they did, and their families learned not to ask.

The base closed in 1993, decommissioned as the Cold War wound down and the intelligence community consolidated its operations. But closing a listening post is not the same as erasing one. The antennas stayed up for years, still useful enough to justify maintenance on an otherwise abandoned base. It was not until 2013 that the remaining structures and antenna arrays were finally removed, returning the island to something closer to the emptiness the Navy had found in 1941. The demolition was quiet, unremarked -- fitting for a place whose entire purpose had been to listen without being noticed.

On March 31, 2011, Skaggs Island was formally transferred to the San Pablo Bay National Wildlife Refuge, a 13,000-acre preserve established in 1974 to protect migratory birds, wetland habitat, and endangered species. The conversion was a return to origins. The tidal marsh that had been diked, farmed, militarized, and abandoned was once again managed for the birds that had always used it -- the egrets and herons and shorebirds of the Pacific Flyway, indifferent to whatever signals had once passed through the air above their feeding grounds. One artifact of the military era persists: the VORTAC radio navigation beacon, identifier SGD, frequency 112.10 MHz, still broadcasts from the island. It is a medium-power facility used by aircraft for low-level enroute navigation -- a final transmission from a place built to intercept them.