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.