National Geographic reveals the unexplored environment of the California redwoods in an epic, year-long exploration. Obsessive redwood climber Steve Sillett of Humboldt State University investigates their monster crowns, tallying biological material and discovering new record-breaking trees, while escaping falling branches and crashing trees in the process. Down below, National Geographic Explorer-in-Residence Mike Fay charts the redwood range to size up the past and future of these primeval trees threatened in 21st century California
