It was a Rock Music Festival on a farm there (a reader says between 187 and 205 Peka Peka Rd) during Easter on 11 April 1971. Bands included Highway, Sons & Lovers, Creation and Kal-Q-lated Risk. But it and Peka Peka itself became known as the NZ version of the infamous festival at Altamont (near San Francisco in December 1969) as a result of the violence that erupted between the Mongrel Mob gang and the Satan’s Slaves biker gang.
According to a report in the university newspaper Salient the following week:
The bulk of the “audience” were there to drink in the sun and watch the crowd, and listen to the music when it was good. They probably soon got bored. At least as the afternoon wore on many were waiting for the fighting they knew would break out. Looks like they weren’t disappointed.
A little extract from the book Patched: the history of gangs in New Zealand by Jarrod Gilbert: