There is already a cache of ours in this forest, Higgins Hidden Valley #3: Bluegum Forest, but I thought that particular part of the bushland is just the tip of the iceberg and a greater appreciation of it can be gained on the way to GZ. Some people may be put off by doing a series, although you can do those in isolation anyway, but this is there to encourage more appreciation of the forest. As this is not declared National Park there is always a risk of rezoning and development but with greater awareness of its existence, hopefully this is just a very remote possibility.
There is a sign not far from GZ with the following information: "All the plants in this area form a very rare community called "Blue Gum Diatreme Forest". The significant tree species is the Sydney Blue Gum (Eucalyptus saligna) The reason for the unique forest community growing here is the presence of deep clay, volcanic soils produced by weathering of the Hornsby diatreme. The diatreme formed over 145 million years ago during the Jurassic period when hot magma from the earth's mantle came into contact with underground water causing a gaseous explosion. It is about 1.5km long and covers an area of about 44 hectares."
A few hundred metres past GZ heading downhill you can actually see where the bluegum forest merges into the dry forest. The change is distinct. A good spot for a geography or biology excursion.
The track in from Westleigh has lot of steps. The alternative from Vale Road Thornleigh is flatter but you may miss a lot of the beauty on the way. The cache is a nice old ammo can to try and counteract the plague of micros in this part of Sydney. It's hidden in the obvious spot although well-hidden. GPS coordinates are tricky here so trust your caching instincts. No more than a step from the track. Please look after the bush and don't bushbash.
And considering the number of dull drive-by micros around why not show what sort of caches you really like by giving this cache a favourite point? I'm sure you've got plenty to spare!