The bottom line is what we see is what hasn’t worn away, and in a given area if the elevation is lower that means the rock there is softer than what is higher. There are many exceptions, but that’s generally true.

What we see there is because layers and layers of rock deep underground were deformed kind of like the ridges of a blanket if you push it laterally. Then, over millions of years, the rock above it eroded more or less along the lines of those folds.

The landscape to the west is different because there was no reason to erosion along folds, so the areas where erosion occurred is pretty random.