Creating cliffs is very simple if you know how to use the displacement tool, you just have to get used to doing it sideways on.
First of all make a brush that will become your cliffs
Now select the cliffs and bring up the displacement window, select how detailed you want it to be by changing the value in the Power box, I chose 2 for this example.
If you use it now the brushes will raise up, you need to change the axis to Y or X depending on the direction you want.
Play around with the cliff until you get your desired look and feel.
Finally, if you used a blend texture then some Paint Alpha will give it that extra touch.