The Treasure Hunter House
If you want to find the treasure of a map, first of all reach a moongate and search for "Treasure Hunter" in "Custom Location".
UO Extinction Treasure Chest System
Killing monsters you will find many treasure maps in UO Extinction. Here you can find out what prizes are in the treasure chests.
Consider that any type of monster have a chance to drop a peculiar type of treasure map.
There are 7 different levels of treasure maps. Each of them have a different difficulty level and prizes.
If you want to know what kind of treasures you can find into a treasure chest here on UO Extinction click here
A good free tool for treasure hunters: "UO Treasure Hunter Tools"
Now download a software like "UO Treasure Hunter Tools" then open your treasure map, see at it and search that place on the map of the world on "UO Treasure Hunter Tools". When you find it, you have to see the number of that map and the facet of the map (Felucca or Trammel). Now you can teleport yourself from the house of the treasure hunters (the one in Britain) to the map location.
When you are on the right location you can begin to dig with a shovel. When the treasure chest came out many guardians will spawn trying to kill you...
Have a good luck!