This is the easiest money grind there that l have come across so far.
As the previous poster has said there is 1 Big buried treasure and 3 small. As well as 2 destructible boats and 3 skeletal remains to examine.
I found by accidently logging of after completing the phase event that when l logged back in, the Phase event was reset. Thus l merrily grinded away farming about $300,000 worth of coins, loot and the odd gems. Even if you die, it is worth paying the extra money to resurrect inside the phase event so you can keep on grinding. So long as you don't port back to town, or leave the phase event, you can reset it by quiting inside the game and "LOAD"ing the game again.
On Level N+ with about 75% gold drop bonus, l was earning about 25,000-30,000 in gold per run. Each run is about 15mins or less.
When you enter the event, you start of with 1 shovel. The maximum number of shovels you can have is 5.
There are 2 NPCs in the event who sell shovels. One for 1000 gold and another for 5 crab claws which randomly drop of the crabs that spawn within the event. The Crab boss in the North East Corner drops another Shovel and the 5th shovel is next to the npc which sells one for 1000 gold.
But you only need 4 shovels. So save your 1000 gold and just farm the crab claws to get the 4th one.
There are 3 bosses. The Crab king - slow moving tank type boss surrounded by 4-5 small crabs, and the 2 pirates next to the treasure chest - one does range damage with a pistol and the other is a melee with a sword.
When you go near the treasure chest, it disappears and the 2 pirate bosses activate. They also spawn mini me's of them selfs until they are both dead.
Looting the treasure chest will spawn big X on the ground with "Dig here". There is 20 buried sites to choose from. There is 1 big treasure chest which has a load of coins and sometimes a lucky coin, epic item, rare item or gem. There is also 3 small treasure chests which just has coins.
I have farmed this over a 4 day period and found the chests all spawn in the same spot. It may vary depending on your own game. But it is easy to find them. Once you have the 4 shovels (go buy the 5th one till you know all the locations), take a screen shot of the map and save it. Load it into a image editor and then go around all the sites till you find all the locations. Once you run out of shovels, QUIT, and LOAD the game again. It should take 5 resets to check them all out.
the map shows the locations of the chests for me. The white dot is where the Big Treasure chest is. Pink is where spare shovels spawn.