Based on the magic enchanted within the Glyphed Oaken Branch, its delivery to the Cenarion Circle in Thunder Bluff is the next step the tauren druid sought. Seek one of the druids there for assistance.
The lifeless hand of the tauren druid clutches a surprisingly healthy looking oaken branch. Examining the branch reveals glyphs of a druidic nature carved into the bark.
As you grasp the branch, you notice it is warm to the touch, more than it should be. The image of Thunder Bluff in Mulgore enters your mind - Elder Rise specifically - and the words "Cenarion Circle" are on the tip of your tongue. It would appear that the suggestion of where to take the branch has been placed within it.
This is from Mulgris, you say? We had heard he sought to minister to the creatures suffering in the Plaguelands, but this is most unexpected... and most saddening. Mulgris is... was a good friend. I will mourn his passing deeply.
His efforts have not gone in vain, thanks to your diligence. In this branch, much lore is stored about the plague the Scourge propagates upon the land. We will study it diligently. As for you, please accept this. It is the least we can do for your noble efforts.