Not sure. There are A mearnsii in the area which it is not; also there were Cootamundras and hybrids which volunteers tackled. Perhaps A. parramattensis or a hybrid of it? It doesn't look like a straight A. decurrens. There are several similar smaller trees downhill of this mature tree.
The whole complex is super variable unfortunately. I suspect this lot would be easier to show you in the field. I'll let you know next time in on Majura!