It's an island between SF and Oakland. Some people live there, probably in the few thousand I'd imagine. Very few businesses on the island.

As others have said it’s part of Yerba Buena island, essentially a landfill project built initially for Golden Gate International Exposition (Worlds Fair like) as a celebration of the recently opened Bay Bridge and the Golden Gate Bridge. It sits between the two sections of the Bay Bridge between Oakland and San Francisco. https://en.m.wikipedia.org/wiki/Golden_Gate_International_Ex...

It was used by the Navy during the war and up to 1997. After that management, and I think now ownership, of the island was transferred to SF. It’s been used as lower cost housing for the City, as well as other things. I saw a recording of Battle Bots there once for example. If anyone watched the show OA, the psychotherapy ward scenes (season two I think) were filmed in one of the cool looking buildings there.

I had friends who lived there after college, I’d say it feels very isolated. Before the new eastern span of the Bay Bridge opened, the only way on or off Yerba Buena and Treasure Island was by car or bus (Bus to SF, car in either direction). Today there is a foot/bicycle path across the Oakland side. There is a plan, yet to be funded, for the western span to get a foot/cycle path connected to SF. https://mtc.ca.gov/our-work/plans-projects/bicycle-pedestria...

It was a Navy base wayback that was used to clean nuclear warships and may or may not be radioactive.

"In April 2013, caesium-137 levels three times higher than previously recorded were found (the island hosted "radioactive ships from Bikini Atoll atomic tests and was a major education center training personnel for nuclear war"—the USS Pandemonium (PCDC-1) mockup had begun nuclear training in 1957."

https://en.m.wikipedia.org/wiki/Treasure_Island,_San_Francis...