It was way too hot and the 'easy' trail wasn't for me, so we abandoned our trip through the streambed to see them from below and opted, the next day, to see the Pinnacles from above.
Soaring like skyscrapers, the pillars are made of old alluvial gravels (conglomerate). The pillars formed as heavy rain washed away softer rock, leaving more resistant rock behind.
In time individual earth pillars (hoodoos) developed, protected by a boulder or hard ,surface on top. Some are thought to be over 1,000 years old.
They are eroding by about 1 centimetre per year. http://www.teara.govt.nz/en/wairarapa-places/page-10
Lord of the Rings fans might recognize these rock formations although our photos are taken from above.
Click here for the Maori account of the original sandstone wall.