The Early Cretaceous Phra Wihan Formation is the second lowest member of the Mesozoic Khorat Group which outcrops in Northeast Thailand.

Comprises fine- to coarse-grained sheet and channelled sandstone beds and rarer variegated siltstone and mudstone.

Deposited in a fluvial environment dominated by high-energy, shallow braided rivers with subordinate lower energy meandering river systems and associated flood plains.

The Phra Wihan Formation is considered to be Berriasian-Valanginian in age based on palynological analysis.

[1][2][3] Sauropod (fossil) tracks have been recorded from this formation.