Police say the victim was found in a grassy area near Fairway Drive and E Street by a pedestrian around 6:20 a.m.
However, it's unknown exactly when the woman, identified only as white and possibly in her 40s, was killed. Detectives said she suffered blunt force trauma to her upper torso and that a dispute may have led to the crime.
Officers said they found the suspect, 47-year-old Jamie Putman, up in a tree, over the body. They got him to come down and took him to headquarters.
"That subject was transported to the San Bernardino Police Department for an interview," said police Lt. Paul Williams. "During the investigation and the interview of this subject, he has admitted to the crime in which the person was, in fact, killed at the scene."
Police said they are not searching for other suspects.
"We're very confident the person we have is responsible for this crime," Williams said.