This time of year the cotttonwoods shed seeds encased in fluffy dander. This cotton litters the forest, coating the ground in white, drifting in heaps alongside the roads and paths. Easily gathered, it makes a spectacular tinder, transforming a spark into instant flame. It burns out quickly, but mixed with birch or cedar bark, or perhaps some shavings of fatwood to give a more sustained flame, you should have no trouble lighting larger tinder and kindling to build an established fire.