From WoWWiki
In the mountains near
Grim Batol can be found the
Great Bulwarks, a series of interlocking peaks with an incredibly high metal ore content. The ley line pattern of this area makes them utterly impassable - all things, from lava flows to storms to travelers must pass around the Great Bulwarks, for they cannot pass through or over them. It is from this
ley line pattern that the Shield Pattern is derived.
MM&M 46