Maritime archaeologists say they’ve discovered the wrecks of two great but long-forgotten ships, along with a newly found “mystery wreck,” just outside San Francisco’s famous Golden Gate.

Researchers with the National Oceanic and Atmospheric Administration discovered the wreckage as part of a two-year project to find and study the vessels hidden in what they call the “graveyard of ships” in the city’s federal waters.

The mouth of the San Francisco Bay is encompassed by the Golden Gate National Recreation Area and, farther out, the Gulf of the Farallones National Marine Sanctuary.

Together in these two regions, archaeologists estimate there may be as many as 300 lost vessels.

“The waters of the sanctuary and the park are one of the great undersea museums in the nation,” said James Delgado, director of Maritime Heritage for the Office of National Marine Sanctuaries, in a press statement.

“These wrecks tell the powerful story of the people who helped build California and opened America to the Pacific for nearly two centuries. Finding the remains of these ships links the past to the present.”

A team co-led by NOAA maritime archaeologist Robert Schwemmer used submersible cameras, sensing equipment, divers, and a wealth of archival material to narrow down and then confirm the presence of the three lost ships.

Perhaps the most famous of them is the clipper Noonday, which was part of the fleet of speedy ships that supplied the Bay Area in the wake of the mid-19th century gold rush.

In 1863, the Boston-based clipper struck a rock off the Farallon Islands and began to take on water. It sunk within hours, after a nearby pilot boat rescued all hands on board.

The prominent rock spire that rises from the islands is known as Noonday Rock in honor of the vessel.

But researchers had to use NOAA sonar data to isolate the location of the wreck under thick layers of mud and silt on the seafloor.

Similarly modern methods, along with historic accounts, allowed to team to pinpoint the remains of a more embattled ship, the steamer Selja.

A cargo steamer that carried goods between San Francisco, China, and Japan, the Selja rammed another ship, the SS Beaver, in heavy fog in November 1910, going down with at least two Asian crew members who remain entombed in the wreckage.

The dispute over who was at fault for the collision — the captain of the Selja ultimately lost — went all the way to the U.S. Supreme Court, resulting in new guidelines for the maritime law known as “the rules of the road.”

NOAA’s underwater survey also included the first sonar mapping of two vessels better known to modern Californians, the tankers Lyman Stewart and Frank H. Buck.

Both having foundered off of Land’s End, in what’s now Golden Gate Recreation Area, in 1922 and 1937, respectively, the vessels are still partially visible to beachgoers at low tide. [Read about another nearby find: “Four-Tusked Walrus, New Whale and 19 Other Fossil Mammals Discovered at California Surf Spot“]

“Buck and Stewart are probably the best known wrecks in the park,” said park historian Stephen Haller.

“We now have a better understanding of how the two wrecks lie next to each other, and what has survived beneath the surface.”

Archaeologists are continuing to study data gathered in the first year of the project, including the identity of the “mystery wreck,” which has been identified so far only as an early steamer tugboat.

[Discover more historic finds in the Bay Area: “ Vinyl Records Excavated at Famous ’60s Commune Challenge ‘Hippie’ Stereotype, Study Says “]

“The shipwrecks off the Golden Gate are places to explore, discover and appreciate our country’s maritime cultural heritage,” said Brian Johnson, deputy superintendent of the Gulf of the Farallones sanctuary.

“Through the study, protection and promotion of this diverse legacy, Americans can learn more about our shared past.”