There's obviously lots of choss but at least in some areas there is also a lot of good quality rock. That whole area of the western blue mtns is all part of the same sandstone belt (Burramoko deposit?? some expert on the list will certainly correct if this is wrong) which has the odd area with some decent climbing :-) (eg Katoomba through Mt Vic and up to the Wolgan). It's the same rock in which canyons form and the good climbing seems to overlay the good canyoning.