This quest is a level 110 archaeology quest that can be offered to reward the mount Spirit of Eche'ro. Players accept the quest from the Archaeology trainer in Dalaran and fly to Thunder Totem to meet with Lessah. She will offer the quest Laying to Rest. Once this quest is accepted, go to the digsites in Highmountain and use your surveying skills in the usual manner. Along with Highmountain Tauren Archaeology Fragments, you will get between 0-5 Bone Fragment of Eche'ro (2 to 3 is typical). You must collect 600 of these to get the mount.
Note that while this quest is up, all three of your digsites will always be in Highmountain. Many of the digsites will be in areas with violent NPC's (such as Darkfeather Valley), but unless you are a brand new 110 with very low gear, you should be OK as long as you pay attention.
Good hunting.
EDIT: Note that Angry Tauren Spirit can spawn when you "loot" an archaeology find, and can also drop the bone fragments. I've been getting between 12 and 16 per kill, in addition to the archaeology fragments.