As the active river carves its gorge, the old channel ends up stranded higher and higher above the active river as the gorge grows deeper. By comparing its elevation to the upstream limits of gorges in river tributaries, it is possible to reconstruct the pre-gorge landscape (top image) and keep the apparently huge gorge depth at the foot of the high mountain in context. Just like the cartoon model a few images back, this “perched” remnant river valley is a nice marker of the where the river used to be before it carved the last 800 ft of gorge in association with the major change in its course.