From publisher blurb:
For thousands of years a great and terrible secret has lain hidden in the depths of the Sea of Silt. In the heart of this vast dust basin, an endless storm of ash and shrieking wind guards the deadliest concentration of evil and power found on the dying world of Athas - the Valley of Dust and Fire.
Valley of Dust and Fire more than doubles the known portions of the world of Athas. Intrepid explorers will discover new wonders and perils within the deadly Sea of Silt, from the beautiful island of Shault to the savage Mountains of the Sun. New rules for traveling the dust basin and surviving its many dangers are included.
With luck and determination a skillful and well-prepared party just might pass through the Great Ash Storm and enter the Valley of Dust and Fire. But this realm of shattered badlands and awful monsters is so deadly that only one man has ever reached the valley and returned to tell the tale.