As the Popo Agie river wends its way down from the glaciers atop Wyoming’s Wind River Mountains toward the city of Lander, it flows into a limestone cave and disappears. The formation, known as the Sinks, spits the river back out at another feature called the Rise a quarter of a mile east, a little more voluminous and a little warmer, with brown and rainbow trout weighing as much as 10 pounds mingling in its now smooth pools. The quarter-mile journey from the Sinks to the Rise takes the river two hours.