Diatomite occurrences in this part of the map sheet occur within strata of the Miocene Fraser Bend Formation of the Chilcotin Group, a dominantly volcanic assemblage which forms part of an overlap assemblage on older terranes.

The Prentice West showing is a white-weathering disaggregated diatomaceous siltstone that is so slumped that dimensions of the occurrence can not be assessed. Microscopic examination shows that the material contains abundant diatoms.