A canyon is a narrow valley with steep walls and a river flowing through it, often formed by erosion.

The key elements are:

* Narrow valley: This indicates a long, relatively tight space.

* Steep walls: These walls are often vertical or nearly so, formed by the erosive power of the river.

* River flowing through it: The river is the primary agent of erosion that carves out the canyon over time.

So, while the word "poorly developed" isn't incorrect, it's not the most accurate description. Canyons are actually the result of a highly developed process of erosion, making them quite impressive and powerful natural formations.