A 14-year-old California boy remains in a coma after telling his father he saw 'snowmen' and 'Kermit the frog' before walking straight off a 120-foot cliff during a hike on Mount Whitney earlier this month.

Ryan Wach, the boy's father, who witnessed the fall, said his teenage son was just out of reach when he fell off the side of the cliff and there was nothing he could do to prevent the fall.

Moments earlier, Zane Wach of Santa Clarita, had begun hallucinating and starting speaking nonsense.

'He told me he couldn’t tell if he was dreaming or not.' said Ryan. 'And then he said he was going to the car. But the car was thousands of feet below us.'

The trouble began on June 10 as the pair summited the 14,505-foot peak of California's Mount Whitney, the tallest peak in the continental United States.