LOS ANGELES (AP) — Nearly two centuries ago, an ex-pirate built a mill that ground corn and wheat for the San Gabriel Mission, part of the chain of Spanish outposts in California dating to the 1700s.

The mill is long gone but on Thursday, crews moved a 15-ton piece of that history from the path of a railroad trench to save it from destruction.

A 20-foot stretch of the brick, stone and mortar millrace that fed water to the mill will go on display at the neighboring Plaza Park, with flowing water recreating the sight and sound of what once was considered high technology.

"It's nearly unique in California, being as early as it is. It's one of the first properties related to the industrial revolution in California," said John Dietler, lead archaeologist for the project.

Spain built 21 Roman Catholic missions in California during its colonization in the 18th and 19th centuries. Many relied on ditches to bring water from rivers, springs or creeks.

"The story of the European colonization of Southern California really hinges around the control of water," Dietler said.

The San Gabriel Mission, about nine miles northeast of downtown Los Angeles, was a wealthy community that had thousands of cattle and acres of wheat, barley and corn, tended by native labor.

"Most modern historians consider it to be forced labor," Dietler said. "They entered the missions voluntarily, typically, but then they weren't allowed to leave."

Enter an apprentice shipwright from Boston named Joseph Chapman, who was captured with a pirate crew that was raiding coastal ranchos. Imprisoned in the Santa Barbara area, he was freed after converting to Catholicism, marrying a Spaniard and becoming a builder, Dietler said.

Chapman designed and oversaw construction of a New England-style grist mill for the San Gabriel Mission, a device that was "revolutionary for its time and place," Dietler said.

Built by native labor and completed in 1823, it channeled water from San Gabriel Valley foothill springs. Closed in 1834 under Mexico's rule, the mission deteriorated for years before it was returned to the church. The remains of the mill were bulldozed for a housing development in the 1940s, although its foundations remain under a street, Dietler said.

In 1998, San Gabriel Valley governments formed the Alameda Corridor-East Construction Authority to renovate rail lines in the region to reduce traffic congestion. Plans included lowering rail lines into a 30-foot trench near the mission.

An archaeological survey of the route began in 2009. At the time, the only trace of the millrace was "a couple of rocks sticking out of the ground and some bushes," Dietler said.

The dig uncovered tens of thousands of pieces of pottery, beads, cow bones and other artifacts, along with the millrace. Once several hundred feet long, only 30 feet had survived. Twenty feet could be saved but it required government funding and heavy-moving specialists.

"I've never done anything like this before," Dietler said. "You can pick up an artifact pretty easily but not this 30,000-pound foundation."

Dietler said the artifact may remind visitors of the efforts of Spanish, Native Americans — and one New Englander.

"These three cultures came together to build this thing that really helped out their community," Dietler said.