Seattle dodged a bullet when it dropped the cut-and-cover tunnel option for the Alaskan Way Viaduct Replacement Project. That's because the project would have sliced through Seattle's waterfront at a point where it is virtually one long archaeological site.
And that tunnel would have been at a depth where it would have done damage to anything in its path (from possible native burials to the tailings from Henry Yesler's sawmill), forcing builders to pick their way through boobytraps of important finds. The deep-bore tunnel, which is now planned, would have a big impact underground, but most of it would be too deep to have an adverse impact on the archaeological layers that document human history. In short, it detours around many problems.
But there could be archaeological issues at both the north and south ends, where the tunnel goes into and comes out of the ground, according to Kevin Bartoy, WSDOT's cultural resources specialist for the mega-projects. Digging here passes through the shallow layers of prehistoric and historic Seattle. The North end comes out in an area that was a major native route linking Lake Union and Puget Sound via what we know as Lower Queen Anne.
This was also an important area in the pioneer period and early industrial Seattle, and some of the area was filled in from the Denny Regrade project, meaning it could contain a revealing mix of historic materials. The jumbled fill itself could yield some interesting finds because a lot of stuff was left behind and washed away with its hills. But also, fill can protect layers that came before.
That said, the area where things are going ahead is at the south end, the so-called South Holgate-to-South King (H2K) section of the project. This is where old Viaduct sections will be removed and the new Highway 99 built, where utility lines are being relocated, surface improvements made, and where the south tunnel portal would be, assuming there is a tunnel. Digging, pile driving, soil work: all could impact potential historic and archaeological sites.
From an archaeological standpoint, this stretch of SoDo, just south of Pioneer Square, and mostly west of First Avenue South, typifies many of the opportunities and complexities that signify how what lies under urban Seattle can be so, well, complicated, confusing, and ultimately so interesting. It's best summed up this way, in the words of a WSDOT archaeologist: "Seattle's on top of everything."
First, consider that this area is where the city of Seattle was actually founded, early structures being built on a small point of land called Denny's Island, a peninsula that was sometimes cut off from the mainland at high tide. It was roughly where First and Jackson is now. In addition to early commercial buildings, there were native village sites there, according to old maps. A wharf was built and eventually docks extended into Elliott Bay and the Duwamish River Delta. What we think of as SoDo was water and a vast tideflat.
At the bottom level, then, you have the old delta, and likely remains of prehistoric activities, covered with sand and mud, and later debris. As docks extended southward, the flats underneath eventually filled in with garbage from the ships and the businesses that sprouted, like sawmills and warehouses. Fill dirt also came from surrounding areas, dug out of Beacon Hill during an aborted ship canal dig project to Lake Washington.
Remains of the 1889 Great Fire were dumped onto the flats to clear the way for the new Pioneer Square. Railroads extended lines and trestles out, and people built homes and shops on the docks and the new land that filled in around them. And those structures were replaced by subsequent generations of warehouses, rail yards, industrial buildings, and residences.
In 1875, the Holgate-King project area was virtually all underwater. By the turn of the century, dry land extended south of Royal Brougham to Atlantic. By 1916, it was almost all dry land. And that land was a mix of everything that made Seattle: sawmill tailings; ship's ballast; urban garbage; building foundations; remains of railroads and sailing ships; the debris of Japanese laundries, whorehouses, saloons, blacksmith shops, brewery outlets, turn-of-the-century restaurants, and homes; and the detritus of global trade and boomtown growth. (Check out the wonderful "Waterlines" project at the Burke Museum for a quick overview of the changing shoreline and infill progression.)
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