You'll probably find there are not many zones in that area that are set as raid zones. Meaning, lots of mobs, tough boss, great loot drops.
Keep in mind that when you form a raid (2 or more groups) all exp and loot is turned off, unless a mob is raid-flagged.
I formed a raid for a 3-hour NPC camp in Nek Forest and we killed it, only to find out that the mob was not raid-flagged, and no-one got quest credit. Had to disband into 1 group and camp all over.
With any zone, make sure you research the beastiary to ensure mobs inside are raid-flagged. Otherwise, it will be all for nought.
Try these:
Fallen Gate
Firemyst Gulley
Stormhold (although not a "raid" zone, it has good mobs)
Splitpaw Raid Instance
Rivervale (mobs in the 40's)