One of Salt Lake City's earliest landmarks emerged from the mud at a downtown construction site Thursday, and archaeologists asked for time to study the pioneer relic.

Construction crews working on a walkway under State Street between the ZCMI Center and Social Hall Avenue unearthed the south wall of the old sandstone Social Hall, considered the first cultural center in the western United States.As a big backhoe scraped the wall and crunched what may have been an ell extension at the east end of the building, state archaeologist Ken Madsen and assistant state archaeologist Kevin Jones conferred with Kenneth Kohler, state parks and recreation curator of Pioneer Trail State Park.

"I don't know that there's a great value to this," said Jones, bemoaning the damage the backhoe might be doing. "But we'd like to slow it down so we can look."

Zions Securities Corp. is building the $2 million underground walkway. The project includes doubling the size of the park that has graced Social Hall Avenue since the 1920s.

The property on Social Hall Avenue is owned by The Church of Jesus Christ of Latter-day Saints, and church officials agree that work ought to slow enough that the experts can decide if anything historically significant is buried there, said Zions Securities vice president James Walton.

Jones explained that in many instances, artifacts surrounding an old building are as significant as the building itself. The archaeologists are particularly interested in what might be buried in the dirt inside the building.

As the backhoe dug, a crew member picked through the debris, finding a rusted hook, a horseshoe, masonry anchors and a bottle. They were probably just garbage when they were buried decades ago, but garbage becomes treasure if it illuminates the past.

"I'm excited to see what is there," Kohler said. "You never know. Sometimes you can change history."

Already there has been one big surprise.

The Social Hall's "exact replica," built in 1980 at Pioneer Trail State Park, is a bit too big.

"It's different. We thought we had the original blueprint of the building. But it's smaller," Kohler said.

Social Hall was constructed in 1852 after the valley's pioneers decided that they wanted something more substantial than the willow-thatched bower they had been using for non-religious public functions.

Used mainly for dramatic productions, Social Hall was the first theater built west of the Missouri River. It was also a meeting place, a dance hall, the site of several sessions of the Territorial Legislature and headquarters for the Territorial Fair of 1856.

After a new theater was constructed in 1862, Social Hall became a private school. LDS College was established there in 1886, and the building became a gymnasium 10 years later.

The Red Cross set up camp in the hall during World War I, and the University of Utah used it during 1918 and 1919. After that, the building housed the LDS College's music and speech departments.

The building was razed in 1922 - apparently lopped just above the windows that allowed light into the basement - and then buried with fill to bring the land to current street grade. A small grassy park and monument commemorated the well-used Social Hall.

In 1979, archaeologists dug up a portion of a wall remnant to get a better idea of how to replicate the building at Pioneer Trail State Park. It was then re-buried, and the park replanted.

Walton said photos will be taken of the building as it is uncovered. "We will try to document it as best we can," he said, adding that some of the debris may be taken to Pioneer Trail State Park for more careful sifting.