The Stanislaus County Sheriff’s Department said a water department employee found the body about 11 miles south of the location where Rodriguez' car was discovered.
Little Juliani's body was discovered much further downstream about a week ago.
Juliani was taken from his grandmother's arms on Jan. 18.
Positive identification of the adult body won't be possible for a few days according to investigators.
When contacted by NBC Bay Area, Juliani's mother said she did not want to make a comment about Saturday's discovery.
Hundreds of people came to a public memorial for Juliani this week. A private funeral will be held next week.