"Steep canyon" refers to a narrow and deep valley with very steep sides. It is a term used to describe a specific type of canyon that has very high and almost vertical walls. Full definition
I rented a pair of waterproof hiking boots and braved the infamous Narrows Hike, where I found myself chest - deep in opaque river water as steep canyon walls, well, narrowed around me. (mindbodygreen.com)
After a short stretch along the banks of the Krossá, we ascended gradually above the tree - line into the northern slopes of the Tindfjöll mountains, hiking through an area of steep canyons and towering rock formations. (theexpeditioner.com)
While Autosub6000 was undertaking its missions, the NOC's Remotely Operated Vehicle, Isis, was deployed to map steep canyon walls and collect images and samples that confirmed coral presence and species. (sciencedaily.com)