(fixed) layer problem in map editor

So for the past couple of hours, I've been making little changes to Utah. curious, i looked at the little layer feature in the terrain editor. I didn't have a clue what I was doing and added a new layer, changing the "diffuse" to RockyDirt_01.



Now the land looks like...this. Does anyone know how to fix it? I'm new to the map editor and I know the answer to my problem is probably obvious, but I'm afraid of ruining things even more. For some reason, pressing ctrl+z doesn't undo the change btw.

Edit: I deleted the layer I made and it didn't fix it. However, when I made a new layer and replaced the diffuse with "overlay", it fixed it and stayed fixed when I deleted the layer. The problem is solved, but I still think it's weird...

 

god ate cake and then barfed on utah