Starting in the Colorado Rockies, it winds southwest, flowing through Colorado, Utah and Arizona, straddling the Nevada-California border, then crossing into Mexico before finally emptying into the Gulf of California. The 1,450-mile-long river and its tributaries make up a watershed that supports around 40 million people across the American southwest and northern Mexico. So begins “The American Southwest,” the provocatively titled new documentary from Fin & Fur Films in collaboration with Len Necefer’s Natives Outdoors. First, it follows the Colorado River basin and its wildlife, catching moments of life, death and renewal as the story moves downstream. Though, it is especially relevant here: much of our water, including Salt Lake City’s, comes from the Colorado River basin.