Geology
The Auckland Region is built on a basement of greywacke rocks that form many of the islands in the Hauraki Gulf, the Hunua Ranges, and land south of Port Waikato. The Waitakere Ranges in the west are the remains of a large andesitic volcano, and Great Barrier Island was formed by the northern end of the Coromandel Volcanic Zone. The main isthmus and North Shore are composed of Waitemata sandstone and mudstone, and portions of the Northland Allochthon extend as far south as Albany. Little Barrier Island was formed by a relatively isolated andesitic volcano, active around 1 to 3 million years ago.
The Manukau and South Kaipara Harbours are protected by the recent sand dune deposits of the Awhitu and South Kaipara Peninsulas. Recent basaltic volcanic activity has produced many volcanic cones throughout the Auckland Region, including the iconic Rangitoto Island.
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