Golden Gate National Recreation Area spokeswoman Alexandra Picavet says the boy fell Monday afternoon while hiking with his family just south of Marin County's Muir Beach.
She says investigators are still looking into the cause of the fall but no foul play is suspected.
Three of the boy's family members were with him when he fell, and two were in a parking lot at nearby Muir Beach.
The family is from West Chester, 25 miles west of Philadelphia.
