From PathfinderWiki

The Skittermounds are a series of tall, sandy hills which stretch for miles across the foothills of the Mindspin Mountains in the Hold of Belkzen. While they take up a large swath of land, few travelers pass through or near them, except those with few other alternatives. This is due to the complex series of ankheg nests located within the mounds. Generally, the warring ankheg armies are content to battle each other in their leagues of underground tunnels, noticeable to those above only as a low buzzing. That said, every few years, runoff from intense rain storms in the mountains floods the plain, flooding the tunnels, and driving the ankheg hordes from their homes to ravage the countryside in search of food and angered at the destruction of their underground realm.1

The Skittermounds was the domain of the Skittering Ravager tribe until recently. The orc tribe was destroyed in 4709 AR after an ill-fated attack on Skull Hill.2