The "Nightline" team eventually reached the banks of the dangerous Teklanika River and our guide, Coke Wallace, wasn't sure we could make it across. "It's fairly treacherous," he said. "That's why people who do this trek should know what they're getting themselves into. It can be treacherous at any turn in the road." The river pushes the ATVs downstream, lifting the wheels off the bottom, but we made it.
(Neal Karlinsky/ABC News)