There isn't any secret to this documentary.
By using stock footage and some dynamic animation, National Geo has produced yet another propaganda film about global warming.
Global warming is mentioned continually through out this rehash of old stock footage.
There is no "secret" Yosemite. Only a global warming diatribe.
There is sparse footage of a solo tree and rock climber to hammer home the points of global warming.
Oh, for drama they added the scary nature of "The Great Flake". a sliver of rock that may fall at any moment...within the next million years.
The highlight, if there is one. is the guys caught in an electrical storm while rock climbing.
Look for other documentaries that really show the majesty of Yosemite. Better yet, visit Yosemite in person as it is a truly wonderful experience you will not forget. I have oodles of shots of Half Dome. Go to the gift shop and buy a copy of Moon rise over Half Dome, by Ansel Adams.