Shillong Plateau represents a horst and Rangpur Saddle constitute the corresponding graben as a result of multiple faults. Geologically the Shillong Plateau embracing Garo, Khasi and Jaintia Hills is regarded as part of the Indian Peninsular Shield, cut off therefrom by the intervening spread of the Ganges and Brahmaputra alluvium. Its prevailing rocks have more in common with the gneissic and other rocks of West Bengal and Bihar than with those of the more neighbouring Himalayan sequence.
The Shillong Plateau is made up largely of Precambrian rocks acutely folded and steeply dipping, with an overturned fringe of Mesozoic and Tertiary sediments. The Plateau, a region of frequent earthquakes, is in fact a wedge like obstructive fragment of the Peninsula, trapped between the Himalayan and Burmese elevatory movements. The general altitude of the Plateau is about 1,500m. The Plateau like character is well developed in west and east of Shillong itself. One of the most noticeable physical features is the extraordinary straightness, sometimes for several kilometres, of the reaches of the river gorges. In some cases this feature has been attributed to faults, but in others, more especially in the case of the shallower ones, the joining in the horizontal Cretaceous beds is responsible. [Eunuse Akon]