That odd straight cliff is actually an erosion channel.
This happens when you use channeled erosion in WM and is pretty difficult to fix.
What you can try is playing with the "filter strength" setting in combination with "sediment carry amount" and "rock hardness".
This is very similar to working with TG2, fiddling fiddling and fiddling
Usually I add some thermal erosion and then again I erode the entire terrain a little bit (low time-scale) with standard WM erosion.
This is a huge carved channel though and I'm afraid that in this particular case you can't get it tweaked away without losing the overall appearance of your terrain.
Damn! I still need to send you those couple of nice WM files I have, shame :-/
Well, I hope this helps a little at least.
Cheers,
Martin
