T - Trails
Naturally, when looking for the meaning of a word, I will turn to the Collins Dictionary 
One of the meanings of "trail" as it related to Geocaching is:
A trail is a route along a series of paths or roads, often one that has been planned and marked out for a particular purpose.
For our particular purpose, the planning involves the strategic placement of geocaches to bring people to a particular area, usually following a theme of some kind, which helps the finder to not only "increase the numbers", but to get a feel for the nature of the landscape: how it changes, its geography (and some cases its geology), the scenery (there is ALWAYS scenery - particularly out west) and what might be called the "atmosphere" of the cache location.
If you participate in a trail hunt and do not appreciate these subtleties, then you are probably just playing a numbers game. That could become boring. So stop to 'smell the roses' so to speak.
It is our desire for you to have an enjoyable experience hinting the Opal Muster Trail - so enjoy and take the time to appreciate this great country of ours!
This Cache
You will find this cache in a rock cairn - a pile of stones marking the location of the cache
This cache is part of the Opal Muster Tail established for the Queensland Outback Geocaching Muster (QOGM) 2021 Paroo - one of fifteen caches each of which contain part of the coordinates for the Mystery Cache "Opal Muster Tail Final"
Each cache contains a logbook for you to sign. In addition, there are some "opals" in each cache which must be opened to discover which "opal" has the clue to the final. Record your clues to discover the location of the cache "Opal Muster Tail Final".
The image below is how the original cairn for this cache was constructed. PLEASE RETURN IT TO THIS STATE AFTER YOU HAVE REPLACED THE CACHE.
Keep the cache covered but away from the rocks Their summertime heat could deform the plastic. Especially the lid - keep the rock cover ABOVE the cache so it is NOT touching the lid. Thank you for helping prolong the life of this cache.

Happy Fossicking!