The headwaters are listed as worthy of preservation for their geology - "New Katuku Trig / Pukewharangi Hill Oligocene fossil locality"[1] Most of the rock in the valley is Kotuku siltstone, a massive to crudely bedded, light- to blue-grey jointed, calcareous siltstone.

The upper slopes are mainly Mangiti Sandstone and Patikirau Siltstone, also calcareous rocks.

All were laid on a deepening mid to outer shelf in the Whaingaroan age, about 41 million years ago.

[5] James Burgess farmed almost 600 sheep in the late C19th,[6] having previously been a shepherd on Te Ākau Station, which had included this area.

[8] A 2012 survey found the estuary had a wide band of rushes grading into native forest, with mud crabs, titiko, coastal daisy, makaka, oioi, fescue, marsh clubrush, remuremu, sea primrose, sand buttercup, kowhai, kanuka, miro, tanekaha and hangehange.