This geocache is NOT at the listed coordinates.
What is at the listed coordinates:
-The entrance of the Hidden Valley Reserve
-Queensland, formally New South Wales
You read correct. About 170ish years ago, the listed coordinates were in New South Wales. Queensland wasn't created until 1859. Some of the nearby caches have more details about the creation of QLD and surveying of the border.
1846 Eastern Australia state boundaries
To find this cache you need to collect some numbers. From the parking coordinates make your way to the listed coordinates and entrance to the Hidden Valley Reserve. While walking up the hill count the number of concrete blocks you pass (do not include the ones at the entrance).
A = the number of concrete blocks to your left on route to the entrance.
B = A-3
When you are at the listed coordinates and entrance to the Reserve, you will see two groups of concrete blocks to the left and right of the path.
C = number of concrete blocks to the left of the path incuding the ones on the way up to the entrance.
The top face of each block has metal stamped pins. Both blocks either side of the entrance have the same stamped pins.
D = the number stamped into these pins
S28° 09.AB8′ E153° 28.CD7′
Happy caching!