A river runs through it
In the Morni Hills of Haryana, smooth, rounded stones lie scattered at elevations up to 1,220 meters (4,000 feet). These are not ordinary rocks. They are river gravels, the kind of water-worn cobbles found on the bed of a powerful river. Their presence high in these hills records a dramatic geological upheaval and a river system that has long since vanished. The hills themselves are part of the Siwalik range, the outermost foothills of the Himalayas, composed of sediment eroded from the greater mountains to the north.
The gravels are part of a geological layer known as the Boulder Conglomerate Formation, the youngest unit of the Upper Siwalik Subgroup. This formation dates to the Early and Middle Pleistocene, roughly 1.8 million to 500,000 years ago. The deposits consist of massive beds of conglomerates—pebbles, cobbles, and boulders cemented together in a sandy matrix. The size and rounded nature of these stones indicate they were transported a significant distance by a high-energy, braided river system, typical of the environment at the foot of a rising mountain range. The river that deposited these gravels was a major waterway, likely a precursor to the modern Yamuna river. It flowed before the Morni Hills had risen to their current height.