Tosham Hill range

Tosham hill range (Tusham hill range old spelling), located at and in the area around Tosham, with an average elevation of 207 meters (679 feet), and the rocks exposed in and around Tosham hills are part of subsurface north-western spur of Alwar group of Delhi supergroup of Aravalli Mountain Range, belong to the Precambrian Malani igneous suite of rocks and have been dated at 732 Ma BP (million years before present). This range in Aravalli Craton is a remnant of the outer ring of a fallen chamber of an extinct volcano. Tosham hill range covers the hills at Tosham, Khanak, and Riwasa as well as the small rocky outcrops at Nigana, Dulehri, Dharan, Dadam, and Kharkari Makhwan. Among these, Khanak hill is the largest in area and tallest in height.

It is an important biodiversity area within the "western-southern Haryana" spur of the Northern Aravalli leopard wildlife corridor.

Geology of Tosham hill

The main Tosham hill is an extinct volcano which erupted sometime 732 Ma BP (million years before present). Geologic province of Khanak-Tosham-Dharan-Riwasa-Nigana Khurd-Dulheri-Kharkari Makhwan-Dadam-Khanak is a narrow oval shaped ring dike of eroded extinct volcanoes on the periphery of a collapsed caldera (magmatic chamber) of roughly 16 kilometres (9.9 mi) diameter on its longest Khanak to Nigana Khurd NW-SE axis and 8 kilometres (5.0 mi) on its narrower Dadam to Tosham E-W axis. This sub-surface ring dyke is now buried under the later era soils. Much of the area to the west of ring dyke is covered with Aeolian sand flown from the fringes of Thar Desert. The remaining area is covered under sedimentary alluvium soil of Harka river of Ghaggar-Hakra River system (paleo Sarasvati River) to the north and east, and paleo channel of Yamuna through Bhiwani in the south and east.