A deep narrow passage with steep rocky sides is called a canyon or gorge.

Here's a breakdown:

* Canyon: Typically formed by the erosive power of a river over a long period.

* Gorge: Often formed by tectonic activity or glacial erosion. They are usually smaller and narrower than canyons.

Both terms describe a similar geographic feature, and sometimes the distinction can be blurry. However, "canyon" is generally used for larger and more dramatic formations.