In the third book of the series, the chase takes Miller into the Nuclear Dead Zone and Splinterland, an area that encompasses Siberia. When I think of Splinterland, I think of Tunguska on a larger, massive scale. The godforsaken place is the next step in the progression (or regression):

Enter a wormhole in Hell, come out in the Slicks.
Enter a wormhole in the Slicks, come out in Splinterland.
THE SKIN BAGS