Diablo 3 Act II Walkthrough Part 3: Howling Plateau

Head north from the Sundered Canyon and into the Howling Plateau. Your objectives update as follows:

Shadows in the Desert
Disrupt the Hidden Conclave Ritual
Disrupt the Secret Altar Ritual

Keep heading north and northeast. Shoot Loose Stones along the way, for some gold. Also search for shrines such as a Fortune Shrine for blessings, and treasure chests for loot. The Enchantress tells you that there is another illusion here. The cultists tried to hide their footsteps, but their spells are weak and easily countered. If we follow these prints, we can find their lairs and halt the rituals.

You fight Lacuni Huntresses and Lacuni Warriors as you enter the Howling Plateau. There are also new types of demons in this zone, Fallen and Fallen Overseer, plus the familiar Sand Wasps that you previously saw in Sundered Canyon. The Black Canyon Bridge is on the northern perimeter of this area, but is closed for now.

Secret Altar
From the entry area of the Howling Plateau, follow the trail of footprints southeast, and into the Secret Altar. There is another new demon here, a Pain Monger. This dungeon is pretty small, and soon enough you run into Deranged Cultists performing their secret ritual. Just attack them to stop this ritual. You should find here a green lore item, "The Seven Lords of Hell", who are Belial, Azmodan, Duriel, Andariel, Mephisto, Baal and Diablo.

Hidden Conclave
The Hidden Conclave is towards the northwest side of the plateau. It is also a very small dungeon. Disrupt the Ritual here as well.

Note that while we went into the Secret Altar first, you can choose to do the Secret Altar and Hidden Conclave in any order.

Search for a frightened girl in the center of the Howling Plateau. She turns out to be an illusion. It's a trap! She vanishes, and you are ambushed by Frenzied Hellions, Dark Berserker Champions, and Pain Mongers.

There is also an event in this zone - A Miner's Gold. A miner is standing near some mining lifts. He tells you there is a treasure chest down here, and wants you to watch his back while he hauls it up, and then you can split the rewards. This starts the event:

A Miner's Gold
Protect the crazed miner

There will be a wave of  Fallen attacking as the miner tries to lift the treasure chest, which appears to be stuck. Then, there will be a second wave, this one includes Fallen Shamans. Once the waves of enemies are over, the crazed miner takes what he came for, and leaves you your share in a Resplendent Chest which contains lots of high quality loot including magic items and possibly rare items.