The area was once under a large, shallow inland sea that began to fill in about 30 million years ago. Pressure over time caused extensive uplift, folding and faulting of the Torlesse and Craigieburn ranges. The limestone rock has been eroded by water into the distinctive sculptured landforms.
Kura Tāwhiti (Castle Hill) is the first reserve in New Zealand established specifically to protect a plant – the Castle Hill buttercup. With just 67 plants in existence, the Castle Hill buttercup can only be found within the 6-ha reserve.