To get the quest, you have to go to Mingyun village, shown on the image above, and talk to the old man ghost near the billboard.
Look around Mingyun Village
Find the hidden note inside the broken down house located just south of the old man.
Look for a will (0/4)
You will then be asked to go to 4 different mine locations and fine the wills. These places can be a good mining spot, so be sure to mark them on your map so you remember when they respawn every 1 or 2 days. There are some Noctilucous Jade, Cor Lapis, and some white iron chunks.
The first one is pretty close to the village. Jump into the water and detonate the barrel bomb near the rock walls to open a hidden entrance. The other 3 are pretty straight forward, especially since 2 of them are near the teleport waypoint north of mingyun village.
Find the treasure
Once you finish getting all 4, go to the designated location, and find a big tree. You will then be ambushed by some enemies.
Clear them out and you will be able to claim your treasure. Completing this quest also gives you the achievement "Trees Should Blend Their Roots and Shade, For That Is Where the Home is Made".