When Faith talks about erosion leaving a flat surface, I wonder if she might be thinking about uneven rates of erosion due to different hardnesses of the material being eroded. For example, here's a photo from Monument Park in Arizona:
She might be wondering why the layers of the Grand Canyon have no buried structures like this that were first eroded into this uneven shape, then covered over again by deposition.
--Percy
PS: Do you know how these come about?