The Chasm Creek diatomite showing is located in Chasm Creek valley 500 metres north of its confluence with the Bonaparte River, nine kilometres northeast of Clinton.

The occurence is hosted in the north draining Mio-Bonaparte channel, a fluviatile and lacustrine interlayer of the Miocene Deadman River Formation which is part of the Miocene to Pleistocene Chilcotin Group composed mainly of alkaline plateau basaltic flows. The Deadman River Formation (EMPR Open File 1989-21) is composed of rhyolite ash, tuffaceous sandstone, siltstone, shale, minor pebble conglomerate. The siltstones and shales are commonly carbonaceous and/or diatomaceous.

A 4.0 metre thick bed of impure diatomaceous earth is exposed for 60.0 metres near the base of a Miocene channel filling of the Mio-Bonaparte channel. The poor exposures are within 20 metres vertically of the top of Deadman River Formation (Chilcotin Group) immediately beneath an unusual quartzite pebble and cobble-rich conglomerate.