The Pacific Crest Trail zigzags some 2,650 miles from Mexico to Canada . It cuts through seven national Parks and 24 national forests as it travels through California, Oregon and Washington. Its a trail of ever-changing obstacles - from some of the highest mountain passes in the west to the hottest desert in the country. The two to three hundred hikers who attempt the PCT each year often find out quickly if they have what it takes for the journey ahead.

It is the driest place in the U.S, with some of the hottest temperatures ever recorded. To forecast how global warming could impact this national park if temperatures rose a few degrees, we set out on an expedition through the Martian-like landscape to document the region's unique creatures. See how some scorpions thrive with a biological "antifreeze" running through their veins, plants live underground without water for months at a time and microorganisms exist by eating rocks.

It is one of Earths few landforms visible from space, a World Heritage site, and one of Americas most popular National Park with over nearly five million visitors a year. But at the edge of a chasm, visitors see only a tiny fraction of the Grand Canyons true beauty hidden amidst its stone, its water and its wildlife. Even for scientists it is a place of baffling mysteries. How and when was it actually formed? Why does one of the planets deadliest diseases still endure in the Canyons premier carnivore the majestic mountain lion? What drove one of the largest birds on earth, the California Condor, to the brink of extinction? Why do microscopic colonies of vegetation that bind the desert sand where no other plant can survive take years to regenerate from the pressure of a single human footfall. And finally what of the Canyons earliest human inhabitants? Where did they live? How did they survive? National Geographic Television joins a rare scientific odyssey down the Grand Canyons entire 277-mile length through some of the most treacherous rapids on the planet to try to unlock the mysteries of this great unknown. A select group of scientists and experts will show us a Grand Canyon few outsiders ever see. From the river still cutting through two-billion-year-old stone to the creatures roaming its incomparable back-country, the Grand Canyon still has secrets to tell.

Far in the Pacific, 250 miles from Honolulu, a hidden wilderness teems with life ... the Northwestern Hawaiian Islands. In 2006, the islands were declared a national monument, in large part because of the area's more than 7,000 marine species. In this special, come aboard a voyage led by scientists from the National Oceanic and Atmospheric Administration who are researching disease-plagued coral reefs, endangered monk seals and the millions of birds nesting in the volcanic islands and atolls.

Life-changing encounters with the natural world await you off-road and beyond the tourist spots in a Yellowstone you've never seen. Get into the two million untouched acres where the bison and bears roam free.

Scale the largest granite monolith on Earth, see the tallest waterfall in North America, and touch a giant sequoia, the largest living thing in existence.

Discover this unique and threatened ecosystem, including carnivorous plants, amphibious birds, fish that breathe air and cacti that grow in water.

The stark appearance of Canyonlands conceals life in unexpected places.

A new wilderness emerges in Glacier National Park as the ice melts.

Join National Geographic as we trek between low and high country to experience big game deep in the taiga forest, beautiful subarctic vistas of the tundra, and the challenge of ascending to the top of North America.