Dogs specially trained to sniff out human remains joined the search. They found more than 1,000 bone fragments in a different well earlier this week.
The bones are being sent to the California Department of Justice for possible identification through DNA analysis.
Police suspect Wesley Shermantine and Loren Herzog of murdering as many as 20 people in the 1980s and 1990s.
Shermantine led investigators to the site. Herzog was on parole and hanged himself after learning his friend was giving up the locations.