The gorge cuts through ranges of steep-sided hills rising from 400 metres near the coast to 1000 metres inland. The hard yet brittle greywacke has been showered with volcanic ash and pumice over thousands of years. Vegetation includes canopies of tawa, rimu, miro, totara and nikau palms, together with cover of fern, manuka and kanuka
Retired farmland has progressively been added to the Waioeka Gorge Scenic Reserve and is regenerating at a fast rate. The regeneration of the land goes through many rapid changes, from pasture grass to fern, and then invasion of fern by broadleaved hardwood and softwood shrubs. Illustration of these stages can be clearly seen throughout the Gorge.