Big Horn Canyon lies between the Big Horns and the Pryor Mountains; another dam, another drowned river. Visibility straight down over the side is adequate and the sun is shining--I've boosted the contrast in this photo to make it easier to see details--but ahead over the Yellowstone basin we can't begin to make out surface features along our route of flight. With no visible horizon thermalling is difficult, and trying to roll out on course between thermals is a matter of guesswork; to check our heading we level the wings then wait several seconds for the magnetic compass to settle down. Even level flight is difficult, because we've intentionally burned all the fuel in the right tank to get a true measure of its capacity; with a heavy left wing it take constant attention to the artificial horizon to avoid drifting into a turn.