The Grinder Creek zeolite showing is within an assemblage of rhyolitic and andesitic rocks of Eocene age located west of the Fraser fault and which are correlative with those of the Kamloops Group east of the fault.

The location of the showing is the centre of a northwest elongate tephra layer approximately 20 metres by 300 metres. The tephra, interlayered with andesitic volcanic breccia, is composed mainly of green lapilli tuff. X-ray diffraction of the tuff has identified clinoptilolite-heulandite group zeolites. The cation exchange capacity for this sample (C5) is of 106.0 milli-equivalent per 100 grams.