You are standing right on the alpine fault here. When the fault next ruptures (1 in 3 chance in next 50 years) this area will be torn apart and moved laterally at least several metres or more, as well as up lifted a few, along with probably 400 kilometres along the rest of the West Coast. I hope no one is looking for the cache that day!
Take note that you pretty much have one foot on the Australian Plate and the other on the Pacific Plate here. The fault line is very obvious on the surrounding hills when you look around.