"We started heading down and he's like 'Hey Pao, I'm going to get there first, I'm gonna go faster than you', and I told him, you can't run here, you have to be careful it's very wet."
But Kao, an athletic Volleyball player at Clovis West, High School kept going.
Pao told us; "He was about 15 or 20 steps ahead of me, I couldn't see the impact, but I saw him tumble. By the time we got down there he was already unconscious, he was twitching, trying to breathe for air, he couldn't hear us."
The young man was airlifted to a Modesto Hospital, where he died on Wednesday.
Yosemite Park Spokesman Scott Gediman told us by phone the popular route to Vernal Fall is safe if visitors are careful.
"The recent death of the young man on the mist trail is certainly a tragic event, these are granite steps that go from the Mist Trail up to the top of Vernal Fall, they are a little wet and slippery this time of year."
Kao acknowledges his brother was not being careful, but thinks some safety measures are necessary.
"I think we do need warning signs, there were no warning signs up there. I think guarding rails up there would be really helpful, also."
Just three weeks ago three young hikers from Modesto were swept to their deaths from the top of Vernal Fall, after they ignored warning signs and climbed over hand rails. Gediman says there's only so much the Park Service can do.
"People need to understand it's a wild place and they have to take precautions. And if they do they will be just fine as the majority of our visitors are."