Williamsport, Md. ? You won’t find a mule named Sal in the exhibit, “Building America’s Canals.”

This is a nuts-and-bolts affair that presents families with some of the same engineering challenges the nation’s founders faced during America’s westward expansion. Visitors can construct and operate miniature cranes, locks and aqueducts, and even analyze the costs of various canal systems.

Just because mule-drawn canal boats gave way to motorized barges 90 years ago, don’t imagine there’s nothing relevant to be learned from the traveling exhibit, which is at the Chesapeake and Ohio Canal National Historical Park’s Trolly Barn in Williamsport through Oct. 12.

“That same science, that same harnessing of physics, went into a lot of the things you see today – highways, bridges, buildings – and this is really the start of that in America,” said Edward Mooney, director of exhibits at the National Canal Museum in Easton, Pa.

That museum created the exhibit more than two years ago, and has sent it out on a tour that began in January at the Discovery Center in Murfreesboro, Tenn.

The 1,600-square-foot exhibit includes five colorful activity stations. But children entering through the 11-foot-high wooden lock gates will probably rush to the large, low table that is the centerpiece of the display. The tabletop, 15 feet long and 4 1/2 feet wide, is a green landscape of farms, towns and forests with a coal mine at one end and a city at the other, connected by a winding blue river.