Fresno County sheriff's officials say the family was hiking in the Yucca Flats along Highway 180 when he disappeared Friday morning.
The boy's father told deputies he had helped his son down a steep hillside before going back to assist other family members.
The father said when he turned around, his son was gone and there were slide marks leading into the waters of 10 Mile Creek.
On the fourth day of searching, authorities said Monday afternoon that they located a body believed to be the missing child about 400 feet downstream from where he disappeared.
They're currently working to recover the body from the water.