The western coastline of the ranges consists of cliffs exceeding 300 m (984 ft), interspersed infrequently with beaches. The rugged upstanding topography is formed from erosion resistant ancient volcanic conglomerate and lava flows laid down in eruptions 12�25 million years ago. The ranges are covered in native forest, most of which is in the process of regeneration since extensive logging and farming in the mid�late 19th and early 20th centuries.
In 1894 a group led by Sir Algernon Thomas (the first professor of natural sciences at Auckland University College, now the University of Auckland) persuaded the Auckland City Council to preserve 3,500 acres (14 km2) in the Nihotupu area of the ranges as a bush reserve. In 1895 the national Government vested the land, and several other smaller areas of the ranges, in the City Council as "reserves for the conservation of native flora and fauna". The Waitakere Ranges Regional Park now contains about 39,500 acres (160 km2). The area is also protected under the Waitakere Ranges Heritage Area Act 2008.
Five reservoirs within the ranges supply water to the Auckland region. The ranges receive an average of over 2,000 mm (78.75 inches) of rainfall annually while the corresponding rate in the city is less than half that. As weather systems approach across the Tasman Sea, their path is blocked by the ranges causing a small uplift sufficient for the system to dump.
The area is home to kauri snails, glowworms and native long-tailed bats. Long-tailed and short-tailed bats are New Zealand�s only native land-based mammals. At the northern end of the ranges, Otakamiro Point is the site of one of New Zealand�s few mainland gannet breeding colonies. In the bush are many indigenous invertebrates, including kauri snail, weta and oviparous peripatus (Onychophora) with 14 pairs of legs, and ovoviviparous species of 15 and 16 pairs of legs, none of which are members of any of the five scientifically
