Keeping 1.7 secret is frustrating and hard work. I feel a constant need to spoilerize. Anyway, I added underground ravines.
minecraftblock0
Latest update on ravines, they will be part of the new map generation code, but will work on old maps if you go into unexplored areas (just like tall grass does now). Also, if you delete existing chunks, and re-generate them, ravines/canyons will appear.