While the huge tunnel-boring machine won't start digging under Pioneer Square for two years, the state Department of Transportation (DOT) has taken the unprecedented step of creating a museum for the viaduct-replacement project.

Called Milepost 31, it combines the history of Pioneer Square with the gee-whiz technology of the massive undertaking to dig a tunnel to replace the aging, and now partially gone, Alaskan Way Viaduct.

It's called Milepost 31 because that's the mile on Highway 99 from Fife in the Puget Sound area where the new tunnel will first cross into Pioneer Square. The name was the brainchild of DOT's Chad Schuster.

"I wanted to highlight the uniqueness of the project," he said Thursday, the day Milepost 31 opened in Pioneer Square.

The project, which is costing the DOT $490,000, is divided into four categories: You Are Here, an introduction to Pioneer Square from historical figures; Moving Land, looking about how the land under Seattle was formed; Moving People, Seattle's transportation history; and Moving Forward, the story of the tunneling technology.

The state leased the building on First Avenue South for two years, with the possibility of extending the lease, and hopes to add to it as items are discovered during tunneling. It also plans to have a replica of the boring machine, the second-largest in the world. The center will be staffed by DOT employees.

Many of the items in Milepost 31 came from the Burke Museum, the Museum of History & Industry, the State Historical Society, the University of Washington, black historians and Native tribes.

There are photographs of damage from the 2001 Nisqually earthquake, which put the viaduct's replacement in high gear.

Various panels provide information about times and place. One is about the construction of the steam-powered sawmill in 1852 by Henry Yesler.

Another focuses on the gold rush that saw $174 million handled in Seattle's assay office in the first five years after gold was found in Alaska.

From 1890 to 1900, Seattle saw its population grow from 3,500 to 43,000, the historical panels show.

On display are glass bottles and china unearthed in test digging for the tunnel project.

Giant tubes hold wood chips from the Yesler Mill, tidal mud from a long-ago earthquake, and fill from the Denny Regrade dating back to the late 1800s.

The state plans to start the tunnel dig in 2013 and the tunnel is expected to be opened in late 2015.

Susan Gilmore: 206-464-2054 or sgilmore@seattletimes.com