In the Demon Spawn War (8972 GE - 9493 GE), Siolix was a mining area controlled by the demon lord Zuggtmoy. It was not worked by the demons or any of her soldiers because early mining efforts led to hundreds dying, mostly demons, mutating into raging, uncontrollable and insane monstrosities. This a product of the area's deep rock, Zuggtmoy's adviser in charge of production decided that slaves would tap the area's rich veins of gemstone, copper, and cassiterite; the latter for tin.
Short of the skills of a master healer, the mines of Siolix gave a sickness that could not be removed. The lucky that survived, mutated, the unlucky, food for her green slimes, black puddings, and gray oozes.
- Borri, from his book History of Me - "The Mines of Siolix"
After the Demon Spawn War, Geb had Siolix sealed off.
There are three entrances into Siolix. Each has a fortress garrisoned by huge earth elementals and other earthen loyal to Geb. The earth elementals periodically move through the rock surrounding the area, making sure nothing has dug in.
There is a channel of the Earth Seam encasing the area. It was redirected by Geb and his elementals, becoming a defensive loop around the entirety of Siolix.
Siolix is a haven for puddings, slimes and oozes. They feed upon each other, but given the chance they will leave the overcrowded conditions and get a taste of what is on the outside.