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Omarama Pinnacles  

The Ahuriri River has carved a cliff from a hill on its west bank, made from a mixture of clay and gravel. The rainfall is low here, because Omarama is in the MacKenzie Basin of New Zealand's South Island, in the rain shadow east of the Southern Alps. Most of the water flows down-hill to the west, so these east facing cliffs are only eroded slowly.

The water trickles down and leaches out the clay, but areas of gravel or a cap rock keep the water away from the clay beneath, which survives as a vertical ridge. Eventually the ridge projecting from the cliff face is eroded from behind, leaving a pinnacle. If the rock cap is ever lost, the pinnacle begins to dissolve until another bit of gravel saves it.

The erosion debris at the foot of the cliff now prevents  Ahuriri river floods from cutting into the cliff, which should survive, with its pinnacles,  for many more centuries.

The vegetation is typical Central Otago tussock with spiny bushes (matagauri) mixed with red rose-hips.