The remains and other items were found 45 feet deep in the well on an abandoned cattle ranch near Linden, Calif., San Joaquin County sheriff's spokesman Deputy Les Garcia said in a statement.
After two days of searching the site, investigators, public works employees and volunteers have found more than 300 human bones, Garcia said. The search would resume Monday if weather allowed.
Sunday marked the fourth straight day that remains have been found with the help of a map prepared by death row inmate Wesley Shermantine. He and childhood friend Loren Herzog became known as the "Speed Freak Killers" for a methamphetamine-fueled killing spree that had as many as 15 victims.
A piece of a human skull and bones found Saturday at the ranch will be sent to the Department of Justice in the hopes of identifying them through DNA testing, Garcia said. Dental records identified remains found Thursday in Calaveras County as those of 25-year-old Cyndi Vanderheiden, who disappeared in 1988.
Another set of remains were found Friday in the same area, and the parents of a missing 16-year-old girl have said authorities told them that Shermantine said their daughter was buried in that spot decades ago.
Shermantine was convicted of four murders and sentenced to death. Herzog was convicted of three murders and sentenced to 77 years to life in prison, though that was later reduced to 14 years. An appeals court tossed his first-degree murder convictions after ruling his confession was illegally obtained.
Herzog was paroled in 2010 to a trailer outside the High Desert State Prison in Susanville. He committed suicide outside that trailer last month after Sacramento bounty hunter Leonard Padilla told him Shermantine was disclosing the location of the well along with two other locations.
Crews are expected to be searching the ranch in Linden for several days, at what Garcia has said would be a "slow and tedious" pace. The property, about 60 miles south of Sacramento, was once owned by Shermantine's family.
The Associated Press contributed to this report.