…a massive rift on the edge of the Great Alluvial Sand Wastes.” —p. 5, Dungeon 181
“…a dark and forlorn place riddled with shallow, monster-infested caverns which hold many dangers…” —ibid.
“The last part of the adventure challenges the treasure-laden characters to make the arduous trip across the Alluvial Sand Wastes to the great city of Tyr.” —ibid. This sounds as if the Canyon is on the eastern edge of the Wastes.
“The Canyon of Guthay combines the features of a true canyon and a massive rift. Some immense tectonic disturbance in the dim past caused the floor of the canyon to subside about a hundred feet below the level of the surrounding terrain, while the rocky walls were heaved upward by the same amount. The result is a canyon that is twice as deep as it appears from a distance when one can see only the massive upheaval of bedrock around it. A trail winds down through tumbled boulders to the canyon’s floor, which is a stretch of relatively smooth sand and gravel that varies from 30 to 90 feet wide along its half-mile length. The walls of the canyon are rough and fairly easy to climb, requiring a DC 10 Athletics check. Wagons can be brought down the trail into the canyon, but it’s a difficult, exhausting trek.” —ibid, p. 13
“The elf pointed westward. ‘A path descends into the Canyon of Guthay from both sides,’ he said. ‘It is only three days’ run, but the beasts that live in the bottom have a taste for our kanks.’” —p. 97, The Amber Enchantress. This certainly contradicts the notion that the canyon is a half-mile in length; that would hardly be worth the trouble of building a massive stone bridge over, and the elves (and for that matter Nok’s tribe) would have just gone around. Also, this implies that it stretches from east to west, where it might make more sense for it to stretch north to south. But there could easily be a kink in the road for the purpose of a bridge.