It's been 35 years since the Society for Industrial Archeology first came to Pittsburgh for its annual conference, and to take the measure of how the city has changed since then, check out the group's 1974 itinerary:

A tour of the open hearth furnaces of the South Side's Jones & Laughlin steel mill. The mill closed in 1986.

A tour of the Westinghouse Extra-High-Voltage Test Laboratory in Trafford. The lab closed in 1986.

Lunch at Sarah's Restaurant, serving Serbian and Eastern European food on the South Side for more than four decades. The restaurant closed in 1992.

At least the historic hotel they used as home base back then is still in business as about 200 SIA members return to the Omni William Penn for a four-day gathering this weekend. Of course, back then it was the Westin William Penn.

Few visitors appreciate the past and present glories of Pittsburgh as much as the Society for Industrial Archeology, a motley band of architects, archeologists, engineers, educators, industrialists, historians, students and others with a shared interest -- preserving and studying historically significant industrial sites, structures, artifacts and technology.

This time around, the group will be touring the Oil Heritage region in Venango County, the varied industrial landscape of Neville Island, two centuries of Beaver Valley industry from Old Economy to the American Bridge Company, and much more.

The society, which has about 1,800 members in the United States, Canada and British Isles, also held its annual meeting here in 1993. What keeps them coming back?

"We study American history through the industrial remains of the past," said conference coordinator Bode Morin. "Pittsburgh was the most important industrial city of America, so it's got a lot of important sites and important people associated with them."

The city's transition to a post-industrial economy also is worth examining, said Mr. Morin, a Detroit native who's working on his doctorate in industrial heritage and archeology at Michigan Technological University, where the society is now based.

"Detroit has similar roots to Pittsburgh but has not fared as well in the post-industrial phase, except maybe in hockey."

In 1974, he said, "Pittsburgh was still a heavily industrialized city, and then in '93 when we were back, it was sort of in transition. And now we're looking at a city that has transcended its heavy-industry past and has a number of high-tech and lighter industries."

One place they'll be visiting is Bombardier Transportation's West Mifflin plant, where more than 800 workers make automated people-moving systems for airports and cities around the world.

"Also, it's important for us to see how the heritage of the city is interpreted, so we'll see a lot of museum and historic sites as well," Mr. Morin said.

He expects former steel mill sites will show the greatest evolution.

"In 1974 the Homestead Works was still operating, in '93 it was shut down. And now, to drive through the lifestyle center, it's a very complete and almost shocking transformation."

More changes: When society members visited the P&LE Terminal in 1974 Pittsburgh History & Landmarks Foundation was still trying to figure out a use for it; now conference-goers can dine at the Grand Concourse, opened in 1978. In 1993, members toured the empty, former Chautauqua Lake Ice Co. warehouse, where there's now much more to see at the Senator John Heinz History Center, opened in 1996.

The society, founded in Washington, D.C., in 1971, has about eight active chapters around the country, Mr. Morin said. The one in Pittsburgh -- the only city the society has visited three times for a national conference -- was short-lived.