It’s fascinating what you can find just by digging holes in the Bay Area—the hulks of buried ships, 240 vertical feet of garbage, and now a painstakingly crafted relic of the 1939 World's Fair.

Workers with the San Francisco Public Works department were inspecting a sinkhole on Treasure Island when they made the discovery. It was a large pipe, at first inspection normal, that turned out to be made from slats of redwood trees. The pipe ran for about 70 feet and...

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