The Adelphi showing is located 20 kilometres southwest of Falkland, near Adelphi Creek.
In this area, Upper Triassic to Lower Jurassic Nicola Group sedimentary and volcanic rocks unconformably overlie sedimentary and volcanic rocks of the Devonian to Triassic Harper Ranch Group. These units are intruded by Middle Jurassic granitic rocks. Extensive Eocene Kamloops Group volcanic and sedimentary rocks overlie the older units.
Kamloops Group volcanic flows host agate. The agate occurs as amygdules and veins.