An elderly California grandmother allegedly was cremated in her backyard by her daughter and grandson, who then cashed her monthly retirement checks for nearly a year, authorities say.

Kathleen Allmond, 50, and son Tony Ray, 30, were arrested Sunday after Tehama County Sheriff's officers found a makeshift barbecue containing remains believed to be those of Ramona Yolanda Allmond, 84, who died at her Corning residence of unknown causes in December, Capt. Paul Hosler said.

After the woman's death, which remains under investigation, Allmond and Ray allegedly laid her body on a bedroom floor for a week before moving it to a cement culvert behind the family's residence.

Hosler said the cement culvert had been a makeshift barbecue, used by the family to cook its Thanksgiving turkey several weeks earlier.

"They let her lie on the floor for a week before burning her for 17 hours," Hosler told FOXNews.com. "The two of them did this together."

Kathleen Allmond then allegedly made a necklace with a portion of her mother's skull, which she wore around her neck. Hosler said Allmond later posted a photograph of herself wearing the necklace on her MySpace account.

Allmond and Ray are accused of cashing Ramona Allmond's monthly retirement and Social Security checks. Each defendant is being held on $30,000 bail on felony charges of embezzlement, elder abuse and conspiracy. Their next date in court is Thursday.

Hosler said authorities are continuing to search for a motive.

"I've never heard anything like this," he said. "Who takes their mom's skull and makes a necklace out of it?"

Hosler said investigators were initially called to Allmond's residence on Saturday after her son, who resides in southern California, told authorities he had not been in contact with his mother since December. Later that day, when officers arrived at Allmond's residence, they were unable to contact anyone at home but believed they saw someone attempting to hide in an orchard behind the home. Shortly thereafter, Allmond's son reported that he had received a phone call from his mother's residence and claimed that his sister, Kathleen Allmond, attempted to disguise her voice to sound like their mother.

Evidence removed from the culvert — believed to be human bone and dental remains — has been sent to Chico State University for analysis, said Hosler, adding that additional charges could be filed.

FOX News' Adam Housley contributed to this report.