Jodhpur Group-Malani Igneous Suite Contact of Aravalli range is a geological feature representing the last phase of igneous activity of Precambrian age in the Indian Subcontinent at the foot of the picturesque Mehrangarh Fort in Jodhpur city, the second largest city in Rajasthan after Jaipur. The uniqueness of the geological feature at Jodhpur prompted the Geological Survey of India (GSI) to declare the site as a National Geological Monument. Etymology Malani was the name of a district in the former state of Marwar (Jodhpur) where volcanic rocks were found and thus named as Malani beds (1877). This name underwent several changes over the years, known as Malani Volcanics Series (1902), Malani System (1933), the Malani Granite and Volcanic Suite(1968). Finally, the complete magmatic sequence has been named as the Malani Igneous Suite. The igneous suite marks the last phase of igneous activity of Precambrian age in the Indian subcontinent. Topography and geography Malani Igneous Suite, an integral component of the Thar Desert in Rajasthan, extends at the periphery of the desert, to an area of covering parts of Pali, Sirohi, Jodhpur, Barmer, Jaisalmer, Jalore and Siwana districts of western Rajasthan. In particular, a rhyolite rock exposure in a hillock of height, originally called the "Mountain of Birds", forms the foundation for the imposing Mehrangarh Fort in Jodhpur. The climate here is of extreme desert condition of scorching summer with hot dry winds and arid conditions. The winters are quite chilly. The rainfall is scanty and occurs during late June to September. The average rainfall is reported to be ; extremely variable with a minimum recorded of during the famine year of 1899 and a maximum of during the floods of 1917. Geology The lithological formations of the region classified as upper and lower Vindhyans in the east and Marwar in the west, have been recorded as consisting of a thick series of sedimentary rocks comprising sandstone, limestone and shales. Igneous activity preceded the deposition of these rocks in western Rajasthan in the form of a thick pile of lava, mostly of an acidic nature. These lava and its plutonic equivalent have been noted in the form of granite bosses and sills in Jalor, Siwana, Mokalsar and Jodhpur areas and designated as Erinpura granite and Malani Igneous Suite (pictured). Mehrangarh Fort section in Jodhpur exposes the best Jodhpur Malani Suite contact. This erosional contact is between the underlying youngest Igneous suite