I can only think of six branches off the main South where the rails have disappeared. Happy to be corrected though.
1. The line to Berrima colliery which was an extension of the line to the cement works.
2. The line to a quarry (ballast?) which branched off the same line just beyond the cement works.
3. The Westby branch
None of the three looks right to me but who knows?
4 The Goondah Tramway to the Burrinjuck Dam construction site. A possibility but don't ask me where!
5. The line from Bargo to the Nepean Dam construction site. Pretty comfortable that this is not it.
6. The line to a quarry which branched off near the crest between Exeter and Bundanoon.
I have never managed to find this line although I have also not made a serious effort. Another SITD, I will leave off the Wild part.
P.S. Got locked into the thinking that is was a branch line. There are literally tens of kilometers of deviations down there too!