[5][6] Sezill Creek originates from the western slope of the massive, glaciated Mount Edziza stratovolcano in the middle of the Big Raven Plateau.

[8][10] Their close association with the recently active Snowshoe Lava Field suggests that they may be discharging from a shallow hydrothermal system driven by residual magmatic heat.

[8] Thin tongues of unglaciated pillow lava originating from the Mount Edziza volcanic complex extend into the upper part of Sezill Creek canyon.

The distal end of this pillow flow has been cut by Sezill Creek to form a narrow, 6 m-deep (20 ft) box canyon.

Tuff breccia consisting of blocks and irregular globules of vesicular basalt in a granular matrix commonly underlies the pillow flow.