The Red Hills are a cluster of hills in the Arrida that Will passes in his attempt to find Tug, whom he got separated from during a sandstorm. The hills are flanked on either side by two series of wells and are followed by other major landmarks as well.
The hills are called the Red Hills because of iron and rust in the ground that turn the sand and dirt red. Somentimes the iron ore appears at the surface. Most of the Arridi iron ore used to make weapons is mined from these hills as they are easy to mine and require no tunnels or complex equipment.
These hills end up affecting the usefulness of Will's Northseeker, and cause him to head in the wrong direction; he heads off into the desert, lost.