Hiker in Buckskin Gulch. A hiker considers the towering walls and narrow passageway of Buckskin Gulch, a dramatic slot canyon forged by centuries of erosion through sandstone. Buckskin Gulch is the worlds longest accessible slot canyon, running from the Paria River toward the Colorado River. Flash flooding is a serious danger in the narrows where there is no escape. Paria Canyon-Vermilion Cliffs Wilderness, Arizona, USA