The Motueka Catchment is geologically very complex compared to many other South Island catchments. A wide variety of rock types are present.
Ultramafic and old sedimentary rocks form the mountains at the south-western end of the Richmond Range in the headwaters of the Motueka.
Similarly, the headwaters of the western tributaries of the Motueka, and part of the middle reaches of the Motueka, are underlain by a complex array of sedimentary and igneous rock types including:
The hilly terrain of the Moutere Depression, making up most of the eastern side of the catchment and the Motupiko and Tadmor valleys, is underlain by much younger alluvial sediments of the Moutere gravel formation.
This is a thick (0.7 km near Tapawera), weakly indurated, and deeply weathered gravel of late Pliocene to early Pleistocene age, dominated by greywacke sandstone clasts, mainly <200 mm diameter, in a silt and clay matrix that cements the clasts together.