Yukon Flats
The Yukon Flats are a vast area of wetlands , forest , bog , and low-lying ground centered on the confluence of the Yukon River , Porcupine River , and Chandalar River in the central portion of the U . S . 
<triplet> Yukon Flats <subj> wetland <obj> instance of <triplet> Yukon River <subj> Porcupine River <obj> tributary <subj> Chandalar River <obj> tributary <triplet> Porcupine River <subj> Yukon River <obj> mouth of the watercourse <triplet> Chandalar River <subj> Yukon River <obj> mouth of the watercourse