In 1978, a Californian named Robb Moss, then twenty-eight, went on a five-week float trip through the Grand Canyon with a bunch of fellow river rats. Moss was walking along another water course, the Loch, the stream in the Ravine, at the north end of Central Park. (He wouldn’t run them chronologically; he’d show “The Same River Twice,” then “Riverdogs,” then “The Bend in the River.”) Moss mentioned another film he’d made called “Containment.” When Moss was seventeen, at Palisades High School in Los Angeles, his brother was drafted and sent to Vietnam.