Cottonwood Island, a large island in the Colorado River, within Cottonwood Valley, in Clark County, Nevada. Cottonwood Island was a low lying island about 10 miles long and up to 3 miles wide. It was forested by cottonwoods and also after the spring flood, cluttered with driftwood from the riparian woodlands along the upper watershed of the Colorado River, washed down and caught in the first wide valley where the river slowed and spread out. Cottonwood Island was important as a source wood and of fuel for steamboats on that river and for the early mills and mines in El Dorado Canyon.