Putangirua Pinnacles

These sediments were laid down about 7 to 8 million years ago when the Aorangi range was an island, separated from the Rimutaka and Tararua ranges by a shallow sea. The conglomerates and gravels would have been eroded rapidly from nearby and laid down as large fans of alluvium (river deposit).
The island was eventually submerged, but has been uplifted above sea level again in the last few hundred thousand years. The immediate area around the pinnacles emerged about 125 000 years ago and has been subject to erosion since then. The pinnacles themselves are relatively young, with more intense erosion over the last one thousand years following deforestation. Hard layers within the conglomerate act as protective caps to the pinnacles, which keep them standing tall whilst the neighbouring material is eroded away by rain.

The cliffs show what the inside of an alluvial fan looks like, with a wide range of poorly sorted particles laid down in weak layers. Look for occasional carbonised wood fragments. Along with the absence of marine fossils, these show that the deposits have a terrestrial origin.
Have a look at the pinnacles and idenitfy the hard layers that protect them from erosion at various levels.