From Ashton, drive east on Rte. 47 toward the toothy skyline of the Teton Range, which thrusts up 7,000 feet [2,134 meters]. Keep an eye out to the north for Big Bend Ridge, the western flank of a volcano that erupted 1.3 million years ago.
The road soon curves to the north and drops to the floor of a forested gorge. Stop near the Warm River Bridge to look for trout and for the ospreys, bald eagles, and river otters that feed on them. Driving out of the gorge, you come to a narrow ridge separating Warm River Canyon (right) from the Henrys Fork Canyon (left). Dense forests hide canyon vistas, but an overlook offers a glimpse of the Tetons and a bend of the Warm River. A turnoff 3 miles [4.8 kilometers] beyond leads to Lower Mesa Falls. Along the paved trail to its rim, the sound of hissing thunder rises from the canyon, as far below the river squeezes between columns of basalt, then plunges 65 feet [19.8 meters].
Return to the byway, drive a mile [1.6 kilometers] to the turnoff for Upper Mesa Falls, and follow the road down the canyon wall to a large parking area. A footpath here skirts the ruins of a turn-of-the-century log lodge, then leads to viewing platforms of the 114-foot [34.8-meter] falls. One platform stands at the very edge of the cataract. (In 1981 the hydroelectric industry proposed to dam both upper and lower falls. Fortunately, the plans were thwarted.)
From the falls, the road passes a dozen heavily logged miles of Targhee National Forest (+1 208 652 7442), then joins U.S. 20.
