"This is an unparalleled opportunity for us to look into the community of San Gabriel and really get at the roots of Los Angeles," said lead archeologist John Dietler.
Archeologists have found more than 20,000 19th century Native American and Spanish artifacts.
"I knew this was a rich site from the very beginning," said Dietler. "I have not been disappointed though, it's even in better shape than I expected."
Among the treasures found were thousands of ceramic bricks, including some with animal paw prints in them.
"I just feel like I can touch them and I'm touching the hands of my ancestors, because they touched them," said Anthony Morales Chief Red Blood from San Gabriel Band of Mission Indians. "They physically touched these artifacts and made these bricks with their own hands."
Crews were sifting through more than 300 buckets of Earth a day. Through the dust were relics of a way of life- providing insights into what people ate, how they traded and who they worshiped.
"Provides an opportunity for people to come and view firsthand history in the making," said San Gabriel Mayor David Gutierrez.
Remnants of a water channel, the foundation of an Adobe building, an 1816 silver coin depicting Kind Ferdinand of Spain, religious medallions, beads, tools and animal bones have all surfaced during the dig.
Gabrielino Tongva Tribe members say they understand the need to ease congestion, expand the rail arteries and make the area safer for pedestrians. And they are excited and proud to see what their ancestors left behind-- but hope the dig doesn't yield their remains.
"That is very important to us," said Native American Art Zuniga. "Hopefully they don't come across any, and if they are, we just hope to the creator that they are handled with dignity."
And as a new civilization is built over remnants of an old one- insight into the past provides direction for the future.
"While it's a bit of a tragedy to move these things out of their original resting place, is an enormous benefit to science, because it's able to fund and to enable our excavation and our learning from this," said Dietler.