Police say the bones were unearthed on Sept. 16 by crews working on an Orange County street-car project in the 2000 block of West 5th Street.
An archaeologist that works with the project identified the leg bones and rib cage as likely human and the county coroner's office was called in to provide further analysis.
Once they were determined to be ancient and of Native American origin, the remains were to be turned over to the Native American Heritage Commission for proper burial.
Officials have not determined the sex or a possible cause of death.
The site of the digging is owned by the Orange County Transportation Authority, which acquired the property as part of the trolley project. Construction started about a year ago. In the past the location had at one time been a residential property and later was a scrapyard.
Sept. 16 press briefing by Santa Ana police on bones found by construction crew