The owner of the rental property was checking the property and called police, who arrived around 9 a.m.
"In the backyard there's a hole approximately 4-foot deep by 5-foot long with a bunch of wood piled up on top of it," said Lt. Paul Williams of the San Bernardino Police Department.
Williams said the body was badly decomposed.
"I couldn't determine the sex, the gender, the age of the individual that is in this hole," he said.
Police did not know how long the body had been there or what the cause of death was. Homicide detectives searched inside the residence, garage and backyard for clues.
The body was removed by the coroner's department.
Police could not locate the people renting the home.