The cache is hidden at:
QKTSY SYAPSX DAUN ENLPNNQ SVNGUN MKAJS SVK QNUNJ DKTP
NFQS KJN DKPSX JAJN ENLPNNQ NGNUNJ MKAJS QNUNJ QNUNJ JAJN
The ciphertext above is a cryptogram, which is a kind of mono-alphabetic substitution cipher. It was created using the following table:
You can solve this by hand, or use an online tool. Some free online cryptogram solvers you could choose from are:
http://quipqiup.com/
http://rumkin.com/tools/cipher/cryptogram-solver.php
You just need to paste the ciphertext into the solver and press go.
Some cryptogram solvers (quipqiup for example) ask you for a clue. In this puzzle, QKTSY=SOUTH.
The cache is a black bison 4.5 metres up a tree. It's attached to a dead part of the tree, not too far from the trunk. It is visible from the ground, but you might have to walk around the tree once or twice to see it.
You can check your answers for this puzzle on GeoChecker.com.
WARNINGS: Sometimes there are kangaroo culls in this area. The last few years these have taken place during winter. You might want to check the TAMS website before heading to GZ. Also, snakes have been seen in this nature reserve, so make sure you don't step on a wriggly stick! And of course be super careful climbing the tree.