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At the Exploratorium, we are always experimenting. In this video, watch a close-up vantage of a bicycle trip along Crissy Field in San Francisco's Presidio. At the southern end of the Golden Gate Bridge, a construction project to rebuild the elevated freeway ramp formerly known as Doyle Drive is underway. Senior bridge engineer John Walters tours us through some of the new seismic technologies being installed, including a seismic joint designed to handle several feet of longitudinal movement and a spherical bearing that allows for three-dimensional movement. Walters also points out a temporary structure built over the historic Presidio Pet Cemetery to protect the grave sites while providing a platform for the construction overhead. Obsidian points, Spanish terra-cotta tiles, Prohibition-era liquor bottles—history lies buried underfoot in the Presidio, one of the earliest settlements in San Francisco, occupied in turn by the Ohlone Indians, Spanish, Mexicans, and the U.S. Army. Archaeologist Kari Jones shares tales of recent digs and discoveries in this national park, and explains why most artifacts are dug up only to be reburied.