The Flaming Cliffs site, also known as Bayanzag or sometimes Bain-Dzak, is a region of the Gobi Desert in the Ömnögovi Province of Mongolia, in which important fossil finds have been made. It was given this name by American paleontologist Roy Chapman Andrews, who visited in the 1920s. The area is most famous for yielding the first discovery of dinosaur eggs. Other finds in the area include specimens of Velociraptor and eutherian mammals.
The red or orange color of the sandstone cliffs (especially at a sunset), hence the nickname.
Information based on http://en.wikipedia.org/wiki/Flaming_Cliffs