That's not how I've read both sections and in fact, it's why I'm asking for clarification from Mr. West. Because I don't see how it can be "only" water runoff. So, I'm asking him for clarification in that regards. I can see it being "mostly showing water runoff". But to not show any other types of weathering would require that neither salt exfoliation nor wind nor any other type of weathering to exist in that one section.
If I'm wrong, I'll readily admit to it. However, it's why I'm asking him for clarification for his statement as he is the only one who knows what he meant by his phrasing.