San Francisco is a city built on the bones of its past parties. If you walk through the Marina District today, you’re basically walking on the ghosts of 1915. But it's the 1939-1940 Golden Gate International Exposition—the "other" big world expo San Francisco hosted—that feels like a weird, beautiful fever dream that actually changed how the Bay Area functions. People usually think of these things as just giant carnivals. They aren't. They're massive geopolitical flexes.
In 1939, the world was on the brink of falling apart. War was bubbling in Europe. Yet, here was San Francisco, literally building an island out of mud in the middle of the bay just to throw a party. It was called Treasure Island.
The Island Made of Mud and Ambition
The sheer audacity of Treasure Island is hard to wrap your head around if you’re looking at it from a modern lens where even building a bike lane takes ten years of community meetings. Back then, they just did it. The Army Corps of Engineers pumped 25 million cubic yards of silt from the bay floor into a square-ish lagoon next to Yerba Buena Island.
Why? Because San Francisco wanted to be the "Gateway to the Pacific."
They weren't just showing off art; they were trying to prove that the West Coast was the new center of the universe. The world expo San Francisco planners knew that the age of the Atlantic was fading. They bet big on Pan American Airways and those massive "China Clipper" flying boats. The idea was that after the fair, Treasure Island would become the city’s primary airport. That didn't happen, obviously—SFO won that battle—but the architecture they left behind, like the Administration Building, still sits there looking like a weirdly regal art deco relic.
The Pacific Unity Theme
While the New York World’s Fair of the same year was obsessed with the "World of Tomorrow" and shiny robots, San Francisco went for something more soulful. They called it "Pacific Unity."
The architecture was this bizarre, beautiful mashup they dubbed "Pacific Basin" style. It blended Mayan, Incan, Malayan, and Cambodian influences. Imagine giant stepped pyramids and 80-foot statues like the "Pacific" goddess looking out over the water. It wasn't just about machinery; it was about culture. They had a "Gayway"—yes, that was the actual name of the amusement zone—and a "Vacationland" that tried to sell the idea of the American West as a playground.
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It was effective.
The Art Nobody Expected
One of the most legendary things about this world expo San Francisco event was the "Art in Action" exhibit. This wasn't just paintings hanging on a wall. It was a live workshop.
The big star? Diego Rivera.
He spent months there, right in front of the public, painting the Pan American Unity mural. It’s a massive piece—ten panels, 74 feet wide. If you’ve ever seen it (it was recently moved back to the San Francisco Museum of Modern Art for a stint), it’s overwhelming. Rivera was literally painting his vision of the North and South Americas merging through technology and art while people ate popcorn and watched him work.
- He included Greta Garbo in the mural.
- He included himself.
- He included a giant machine-god that looked like a car engine.
It’s probably the most significant piece of public art to ever come out of a world’s fair, and it almost didn't stay in the city. After the fair, it sat in crates for nearly twenty years before finally finding a home at City College of San Francisco.
The Weird, Dark, and Fun Stuff
You can’t talk about a 1930s world expo without acknowledging how weird things got. They had "Sally Rand’s Nude Ranch." I’m not making that up. It was exactly what it sounds like—a Wild West-themed show where women wore... not much. It was the most popular attraction at the fair.
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There was also a miniature city called "Midget Town," which is a reminder that the "good old days" had some pretty questionable ideas about entertainment.
But then you had the Tower of the Sun. It was 400 feet tall. It had a carillon of 44 bells that played music across the bay. At night, the entire island was lit up with colored floodlights—pinks, ambers, and blues—making it look like a floating jewel. This was at a time when most people still had single lightbulbs hanging from their ceilings. The visual impact was tectonic.
Why it Matters in 2026
You might ask why a fair from nearly 90 years ago matters now.
It’s about the infrastructure. The Bay Bridge had just opened in 1936. The world expo San Francisco was the debutante ball for the bridge. It forced the city to think about the Bay Area as a connected region rather than a bunch of isolated towns.
Also, look at the tech. Television was demonstrated there. It was one of the first times regular people saw a "moving picture" broadcast through the air. In a way, the Silicon Valley spirit of "look at this crazy thing we just built" started on that man-made island.
The Reality of Treasure Island Today
If you visit Treasure Island now, it feels halfway between a construction site and a ghost town. They are building thousands of new homes there. But the wind still rips across the flats just like it did in 1939.
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The soil has been a nightmare to deal with. Because it’s all landfill, it’s prone to liquefaction. Plus, the Navy used the island for decades after the fair, leaving behind some toxic leftovers that have taken years to clean up. It’s a complicated legacy. It’s a reminder that when we "conquer" nature to build something grand, nature usually sends a bill later.
Honestly, the fair was a bit of a financial flop compared to the 1915 one. It lost money. But culturally? It’s why San Francisco feels like a Pacific hub rather than just another American port.
Misconceptions About the Fair
A lot of people confuse the 1939 fair with the 1915 Panama-Pacific International Exposition.
The 1915 fair gave us the Palace of Fine Arts—that big domed building near the Golden Gate Bridge. The 1939 fair gave us Treasure Island. People also think the fair was closed because of the war. Actually, it ran its full course, though the 1940 season was definitely overshadowed by the Nazi invasion of France. You could feel the shadow of the real world creeping over the "Pacific Unity" dream.
Actionable Steps for History Buffs
If you want to actually "experience" the world expo San Francisco today, you don't need a time machine.
- Visit the Treasure Island Museum: It’s located in the original 1939 Administration Building. It’s small, but it’s packed with artifacts, including old uniforms and architectural models.
- See the Rivera Mural: Check the SFMOMA or City College of San Francisco schedules. Seeing the Pan American Unity mural in person is a religious experience for any art lover.
- Walk the Marina: While this is mostly the 1915 site, you can find plaques and architectural nods to the city's "expo era" scattered throughout.
- The "Bells of the World": Some of the carillon bells from the Tower of the Sun are actually still around. Researching their current locations (some went to churches, others to universities) is a fun rabbit hole.
San Francisco is a place that constantly reinvents itself. We’re seeing it again now with the AI boom. But the DNA of that reinvention—the idea that you can just pull an island out of the water and declare a new era of unity—that’s pure 1939. It was a moment of radical optimism right before the world went dark. That's worth remembering.
When you're looking at the skyline from the Bay Bridge, look at that flat stretch of land to the north. That’s not just an island. It’s a monument to the time San Francisco decided to invite the whole world over for a drink while the house was on fire.
Go visit the museum. Look at the old photos of the "Court of the Seven Seas." You'll see a version of the city that was bolder, weirder, and maybe a little more hopeful than the one we have today. It’s a good reminder that the city is always capable of building something out of nothing. It's literally what we're built on.