Except for a few hills in the northeastern corner, the region is primarily gently undulating land, most of it varying in elevation from 90–180 metres (300–590 ft), tilting from the Phetchabun Mountains in the west down toward the Mekong River.

Much of the surface of the plateau was once classified as laterite, and layers that can easily be cut into brick-shaped blocks are still so called, but the classification of soils as various types of oxisols is more useful for agriculture.

When portions of the plain uplifted as a plateau, these relict soils, characterized by a bright red color, wound up on uplands in a great semicircle around the southern rim.

This began to change when the golden age of Lao prosperity and cultural achievements under King Surignavôngsa (สุริยวงศา Suriyawongsa, ສຸຣິຍະວົງສາ /sú lī ɲā ʋóŋ sǎː/) (1637-1694) ended with a successional dispute, with his grandsons, with Siamese intervention, carving out their separate kingdoms in 1707.

The arid hinterlands, deforested and depopulated after a series of droughts likely led to the collapse of the Khmer Empire, was only occupied by small groups of Austroasiatic peoples and scattered outposts of Lao mueang in the far north.

[citation needed] In 1718, the first Lao muang in the Chi valley—and in fact anywhere in the interior of the Khorat Plateau—was founded at Suwannaphum District, in present-day Roi Et Province, by an official in the service of King Nokasad of the Kingdom of Champasak.