The Deccan Trap geology of Bombay (Mumbai) differs from the main Deccan flood basalt province in several ways. Very few geological, geochemical and geochronological studies exist on the Deccan geology of Bombay. The basalt of Gilbert Hill, Andheri occupies a special place in Bombay geology on account of its spectacular columnar jointing, more than 50 m high, and for this has been designated a National Geological Monument by the Geological Survey of India.