Much of the following notes are taken from the document "Historic Assesment: Onoke Ballast Pit" by Maria Butcher (April 2011) which was commissioned by the Department of Conservation - www.doc.govt.nz/pagefiles/72064/onoke-heritage-assessment.pdf.
It is not known exactly when the Onoke Ballast Pit opened however there is some evidence of it operating from around 1878, when work on the Whangarei to Kamo railway section of railway began, until 1937 or 1938 when it was officially closed.
Scoria ballast was produced at the quarry, located on a volcanic cone, before being crushed on site then moved from the quarry to the railway using a self-acting incline which was one of several safety hazards noted with the Ballast Quarry operation. Official letters and reports in the local Northern Advocate newspaper detail many accidents relating to both the self-acting incline transport system and the quarry operations.
The track from the road is slowly being cleared and is, at the current time, easy to follow through the regenerating bush to the main junction where the incline track heads off to the left. The track to the right leads into the quarry area which is being reclaimed by the regenerating bush. The quarry operation was carried out by the traditional method of blasting then digging scoria from a near vertical face as well as the use of drives and tunnels into the hillside. There are two drives still evident today, although a bit of exploring will be required, both starting close to each other in the back right hand side of the quarry area but diverging as they progress into the hill side.
Each canyon like drive terminates as a tunnel. The eastern drive ends in a tunnel, more like a small cavern, which is only a couple of meters long as it appears that part of the original roof has collapsed into the cutting. The western drive, where the cache is located, is well defined and ends in a tunnel which is much longer. This tunnel can be easily explored if you have a torch and it is interesting to see the manual work that must have been involved in recovering the scoria ballast. The inhabitants – from the cache name – are harmless but can be un-nerving. It is impossible to determine the actual length of the western drive’s tunnel as the roof has partially collapsed some distance from the tunnel mouth and the collapse has made the remaining tunnel entrance too small to gain entry.
Due to the vertical, and narrow, canyon-like sides to the western drive it is not possible to get accurate GPS co-ordinates. The cache is located just outside the tunnel entrance; attempt to minimise any damage to the environment when searching for, retrieving, and re-hiding the cache. Please also re-hide the cache carefully as the reserve is often visited by local children.