The spectacular Tangarakau Gorge consists of erosion resistant sandstones and minor embedded mudstones of the Mokau Group, originally laid down in shallow seas about 15 million years ago. As these sedimentary rocks were uplifted, rivers became entrenched in the emerging land surface. Where the rocks were soft, the rivers formed broad open valleys, but where resistant rocks were encountered, such as in this locality, steep sided gorges were formed.
The bends in the Gorge reflect the meanders of the original valley. This Gorge terminates at the 50m high Te Rerepahupahu Falls on the Waitaanga Stream, the major tributary of the Tangarakau River, and upstream of the Falls the stream has a winding course through shallow swampy ground, the remains of the original valley.
Swamps, which existed at the time when the sediments were deposited, formed peat, which were buried and compressed to form extensive coal seams. The coal has been commercially mined in a number of localities, and a small outcrop is visible in the road verge on the opposite side of the road.
There is more information on the nearby Heritage Trails noticeboard at the parking coordinates.
By the way, have a look down from the bridge to notice the old bridge and figure out how they got to the western end.
The cache is a 400ml plastic jar.