The YBI Shell Midden Project - Preserving History

More than a thousand years ago, long before there was a Bay Bridge, the Ohlone Indians would often camp on the eastern side Yerba Buena Island, particularly during the winter months. Refuse from their encampment built up over many centuries and turned the soil into a dark, blackish color interspersed with shell and bone, referred to as shell midden.

The island was turned over to the U.S. Army when California became a state. Squatters settled on the island in the 1840's until the army occupied the island in the 1860's, both leaving remnants of their occupation with that of the Ohlones.

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YBI Shell Midden Photo Gallery

It was not until the 1930s when excavation began on a tower footing for the existing bay bridge that some secrets of the Yerba Buena shell midden were unearthed. But only a small portion of the midden was excavated since the builders dug no further than the size of the holes required for the tower footing. Very little archaeology was done in connection with the construction and, to make matters worse, the archaeologist's excavation report was lost in the passage of time.

The greater part of the midden's secrets remained locked in the soil until late summer of 2002 when an archaeology team under the direction of Caltrans' Toll Bridge Archaeology Manager, Janet Pape, began an archaeological investigation in advance of construction of the new East Span bridge footings. As is their policy, Caltrans also contracted with an Ohlone to be on site to provide input in case Indian burials were discovered.

The first task facing Caltrans and its archaeology contractor, URS Corp., was to find the boundaries and depth of the shell midden by taking 2-inch core samples from the area. When the Army occupied the island, they leveled the sloping hillside to make a parade ground, thus covering the midden with four to six feet of soil, according to Cindy Arrington, Principal Investigator for URS Corp.

The soil also held something else - utilities. It was necessary for the crews of Silverado Construction Company to relocate utilities connected to nearby former residences of military officers, including Admiral Chester Nimitz, and a defunct firehouse, demolished earlier in the summer.

Meticulously excavating small test pits by hand beneath the bridge and carefully sifting soil through wire screens, the URS archaeologists began a recovery of information and artifacts - obsidian flakes and arrowheads, a small bowl mortar (most likely used for grinding herbs for medicine), bone awls, and animal bones.

All the artifacts from the archaeological excavation have been sorted and catalogued at a URS facility. Some of the older and more obscure artifacts have been dated using such methods as carbon dating and other techniques. Some items date to 1200 BC.

Crews also found ample evidence of the remains from both an 1867 Army guard house and a family who once lived on the island for several decades prior to the Army's arrival. These items included brick rubble, a worn whetstone, broken glass, square nails, an 1877 dime, and a token inscribed with the date of "1854." Also, a large section of redwood planking was found in near-perfect condition. This planking was likely laid down by the Army. An 1871 photo of the Army occupation of Yerba Buena Island depicts a wooden walkway around the parade ground and down to a wharf, now long gone.

The information gathered about where the artifacts were found in each square pit that was dug by the archaeologists will be further analyzed to reveal more secrets about all the people who lived on this site.

There will be an exhibit about the archaeology and history of the site once all the information has been analyzed. Stay posted for where and when.