My thorium rotation was always in Winterspring, but as mentioned above, I don't know how crowded it may be these days. If you do go there, be sure that your rounds also include going into the elite dragonkin cave in the hills SW of Everlook, and the yeti cave directly east of Everlook. I also usually find one mine in the gorge with the elite giants in the far south (the ramp down is to the west, on the north side of the bridge).

If you're particularly looking for just rich thorium veins, then I would recommend wowhead as well to find them. My rotation was just for any thorium veins I could find.