Interesting find Julie - Golden Wattle was planted on Mugga Mugga by Charles Weston as part of a white plantings in the 1920s (the whitish stem is clearly evident in your photo) but I have never seen it naturally south of the Lake. Do you think it is planted on Farrer Ridge?
It hasn't been planted there are up to twenty smaller ones scattered around that area. I can't recall seeing them prior to the control burn that was done about 4 years ago its a very gravelly area with not much growing there. Nearby are Acacia Melanoxylon and A..boormanii. I have seen A.pycnantha on Mt Jerrabomberra near the summit and Nancy Burbidge in her Wattles of the ACT notes seen on Mt Jerrabomberra and Mt Mugga Mugga
The CNM location records list Wanniassa Hills but there is no matching record. Friends of ANBG Fronds magazine has an article on golden wattle saying it was collected by Charles Weston on Mt Jerrabomberra in 1917. The ones on Mt Mugga Mugga are likely descendants of the Weston plantings.