Escarpment
Definition: a long cliff or slope that separates two flat areas of differing elevation
This geographic feature normally happens due to a fault line or erosion.
Why I Looked It Up
Some of the earliest evidence of butter production is found in an unlikely place: an immense sandstone escarpment where the borders of Libya, Algeria, and Niger meet.
Postscript
Added on
Weirdly, I was looking back in my notes, and I found another reference from On the Move that I hadn’t worked through yet.
In St. Bernard Parish, the thin escarpment of delicate soil still extending east from downtown New Orleans and the levees of the Mississippi River, the population has decreased 39 percent.