Once there, speak to the Great Ritual Priest Zahmut. Ask about going into the Mesa and accept his offer and you will be taken to a large structure with three ghosts standing before it. Speak to the Ghosts and each will explain to you what he needs from you.
You will now need to travel to, and complete, the following missions and you may do them in any order you wish. Note: you can actually do the missions first without going to Augury Rock and speaking with Zahmut. Completion of each mission teleports you to Augury Rock, which saves overall travel time especially if you journey directly to Elona Reach or Dunes of Despair first.
Dunes of Despair
After completing those three missions, return to Augury Rock and ask to go to the Mesa again. Step through the Divine Fire (behind the ghosts) and onto the runes on the ground (they will all shine once you step on them if you have completed the missions):
Warning: The following text contains spoilers relating to the plot of Prophecies.
After the Shining Blade were driven to the brink of extinction by the White Mantle, Vizier Khilbron suggests that your only hope of defeating the White Mantle is to achieve ascension. Only then would you be ready to face their hidden masters, the Unseen Ones. You arrive at The Amnoon Oasis in the Crystal Desert with the goal of ascending.
After completing Ascension, you will then be teleported to the Dragon's Lair to meet with Glint and receive valuable advice on your adventure. Completing the Dragon's Lair (mission) takes you back to fight the White Mantle in the Southern Shiverpeaks.