The Bombay hills are a group of hills situated about 30 miles south-south-east of Auckland and form a natural barrier between the greater Auckland urban area and the lower Waikato River basin. Although these hills are virtually the south-western corner of the Hunua Ranges, they are distinctive enough to be identified separately. The township of Bombay was named after the ship that brought immigrants (1863) to settle in Williamson's Clearing on the old military road from Drury to Pokeno. The puriri forest along this road gave cover to the marauders that skirmished in the early stages of the Waikato War. Bombay is situated on top of an eroded volcano (1,030 ft) which, together with other smaller centres to the south, ejected lava to form the steep terrain that inspired the Maori name of Puketutu (steep hill) and the popular name – The Razorback. To the north-west the more gentle slopes which, like those of Pukekohe Hill to the west, were covered with volcanic ash, are today the scene of intensive market gardening. Beneath the lava flows to the north are to be found sandstone and thin coal seams that have been mined for local consumption. The highest point on the hills (1,235 ft) is one mile south-east of Bombay and is of much older sedimentary rock from which manganese has been mined at Pinnacle Hill.
by Leslie Owen Kermode, B.A., Geological Survey Station, Department of Scientific and Industrial Research, Otahuhu.