Low-grade greywacke of the Torlesse rocks (Canterbury Suite) at the southern end of Otira Gorge contains the Oretian-Warepan indicatorHokonuia limaeformisTrechmann, and other fossil localities suggest a simple southward younging of faunal zones between the Zig Zag (Otira Gorge) and Temple Basin. However, the sequence is structurally complex, with generally steep dips; an apparent large, south-closing shallowly south-west-plunging antiform crops out in the west, and a major, steeply plunging, northward-closing fold occurs in the east. A broad fault zone trends north through the Otira Gorge, and several other extensive faults trend north-east.