At the Fairley Kaolinite showing, a 10-metre thick layer of massive white rhyolite ash and lapilli tuff of the upper volcanic member of the Eocene Allenby Formation (Princeton Group) outcrops for 250 metres along the west bank of the Similkameen River, 10 kilometres southwest of Princeton.

The rhyolite is in part altered to kaolinite. Heating tests on a single sample showed a very low pyrometric cone equivalent (PCE). This suggests that alkalies are present, and that the material is not suitable for making refractory bricks. Analysis using x-ray diffractograms show only dolomite and quartz as impurities.