Five km (3 miles) of giant cottonwood trees, with their tangle of thick roots, frame varieties of giant fern to create a canopy of fronds and leafy branches over the road.
There are no cottonwood trees, or trees of any kind here. 
mnli hypothesis: There are no cottonwood trees, or trees of any kind here.  premise: Five km (3 miles) of giant cottonwood trees, with their tangle of thick roots, frame varieties of giant fern to create a canopy of fronds and leafy branches over the road.