that is a very interesting little patch. I can tell you this: prior to about 1880 there was an Aboriginal trackline that runs to that point from behind Woronora cemetery and down to the back of Gymea Bay where Sylvania Rd. that is why Forest Road is not continuous and dog legs at various points. this section has never been a road, its never been useful as roadway, its never been improved much beyond its original trackway which is curious historically. You have the "natural stone bridge" in there, noted by Matthew Flinders