For 28 years, Caitlin Johnson wondered where her mother was.

The Santa Rosa native was put into foster care after her mother abandoned her and her six siblings in 1983. Already estranged from her extended family due to drug addiction, Johnson's mom fell off the map altogether in the early 1990s.

"I always had this feeling she was out there somewhere," Johnson told KCRA. Year after year, she heard nothing. She waited and she hoped.

Then, last year, Vacaville police contacted her. Finally, they had found her mother: A Jane Doe discovered by construction workers near the Vacaville outlets in 1991 was Cynthia Merkley.

The National Missing and Unidentified Persons System, which runs a database of over 13,000 unidentified persons calls it "the nation’s silent mass disaster." Some 4,400 unidentified bodies — colloquially called John or Jane Does — are recovered in the United States annually. By the end of one year, 1,000 of those individuals will still be unidentified.

Merkley was only identified because of a prior arrest and modern forensics. An arrest in 1983 put her fingerprints in the system; recent advances in technology allowed investigators to obtain enough of a fingerprint from her records to find a match in the national database.

Although Merkley has been found once more by her long-estranged family, her fate leaves a lingering mystery; police are still trying to determine how she ended up in Vacaville and what killed her.

In the last 50 years hundreds of unidentified bodies have been found in the Bay Area. Filed as John or Jane Doe alongside a reference number, many of their cases have gone long-cold, while others are still under active investigation. The various counties have differing methods in attempting to help the public identify the deceased. Sketches are often drawn by forensic artists, while skeletal remains are sometimes re-imagined through the process of clay modelling and, more recently, computerized 3D facial reconstruction.

We gathered all the John and Jane Does that were released with imagery across the nine Bay Area counties from the early '70s onwards, to increase visibility in the hope that readers may recognize them.

Each case in the slideshow above is unique, and some of the circumstances under which the bodies were found are hard to forget. One of the earliest John Does on our list may be one of the most beguiling — the partial remains of a boy between the age of 4 and 6, found on the Mill Valley Golf Course in 1974. A ladybug stick pin was found on his clothing. Another unidentified woman's remains were found with the help of a homeless person who had been carrying around her skull in Brisbane. A presumed victim of the "Happy Face Killer" Keith Hunter Jesperson was found in Santa Clara County, but no one was ever able to name her.

When poring over the sketches and recreated busts of unidentified persons, a distance separates you from the faces. The provided information is often brief and clinical: height, weight, race. But as you read the details, their shortened lives turn into something real: two quartz crystals found in the pockets of a Sonoma County woman in 1983; a keychain of the Statue of Liberty and the words "God Bless America" on the body of a San Mateo man struck by a vehicle on a freeway ramp; handwritten journals about math and science near a Rohnert Park man’s remains.

It’s easy to think of the faces only as a part of the past. But each was once known and loved by someone. Somewhere out there may be an estranged friend, child or parent, separated by addiction, circumstance or chance, who wonders every day where their loved one went. Giving them their identities back is the least they deserve — and perhaps the final act of compassion for a lonely case in a county coroner’s office, waiting to be closed.

If you think you may know the identities of any of the faces in the slideshow above, please contact the relevant agencies listed below the images.

Andrew Chamings and Katie Dowd are digital editors at SFGATE. Contact them at andrew.chamings@sfgate.com and katie.dowd@sfgate.com.