Archaeologist Deanna Jones couldn't believe her eyes as she hunched over a shallow pit dug next to railroad tracks in front of the San Gabriel Mission.
She was inside the recently excavated foundation of a long-gone adobe building that once stood in the mission's 40-acre Bishop's Garden, first cultivated in the early 1780s.
As Jones scooped a trowel full of dirt from what had been the adobe floor, a silvery glint caught her attention.
"It looked like a piece of scrap metal at first," said Jones, a 29-year-old Van Nuys resident who has worked four years as a professional archaeologist. "I rubbed it on my jeans and noticed the detail."
With the crust of dirt wiped away, it was clear this was an old coin. A bit more polishing on Jones' pant leg revealed the image of a man's profile, the words "FERDIN VII" and "DEI GRATIA" (Latin for "by the grace of God") and a date: 1816.
For a 30-member team of archaeologists studying the ground where a freight train trench will soon be dug, Jones' Jan. 18 discovery of the silver coin was the biggest so far. The area they are exploring is a narrow strip, roughly half as long as a city block.
"It was certainly amazing to me. It's definitely the highlight of my career so far," Jones said Friday of Spanish King Ferdinand VII's silver coin.
Halfway through their hunt, the archaeologists have recovered some 20,000 artifacts. By the time they finish in mid-March, they predict, as many as 60,000 will have been unearthed and cataloged.
Most are animal bone fragments, said John Dietler, the project's lead archaeologist. But chunks of old pottery, the adobe's foundation, Native American shells and European beads, a religious medallion and railroad spikes left from when tracks were laid in 1874 for Southern Pacific's Los Angeles Division Line have also been uncovered.
Union Pacific now operates the busy line, which is why a $498-million trench is being planned that will lower tracks 30 feet beneath city streets along a 2.2-mile stretch.
Long freight trains tie up traffic when they cross four major San Gabriel thoroughfares: Ramona Street, Mission Road, Del Mar Avenue and San Gabriel Boulevard. And the loud horns they sound as they approach those intersections disrupt much of the city.
The trench project, called Alameda Corridor-East, is modeled after the Alameda Corridor, which went into operation in 2002. It features a 10-mile underground track system for freight trains that connects shipping ports with downtown Los Angeles.
Rick Richmond, chief executive of the Alameda Corridor-East Construction Authority, said the Alameda Corridor peels off in three directions in Los Angeles. One of those legs passes through San Gabriel and neighboring cities.
He said officials have studied 54 San Gabriel Valley rail crossings and targeted 22 of the busiest for improvements. Most of the new grade separations will route automobile traffic over or under train tracks.
But the historic nature of San Gabriel — with the circa-1771 mission on the north side of the tracks and the Mission District on the south — means flyover bridges could not be built above Union Pacific's rails, Richmond said.
Dietler said archaeologists will monitor the trench excavation once construction on the 31/2 -year project begins. Experts will be especially watchful for signs of an old tunnel that supposedly connected a nearby adobe with the mission. Legend has it that the passageway contains treasure.
The public can watch Dietler's team's archaeological work as it is streamed on the authority's website, http://www.theaceproject.org, officials said. Later, the curious will be able to use it to look for the treasure tunnel along with the trench diggers.