The Black Bay Opal showing is located between Robbins and Monte Creeks, approximately 30 kilometres south east of Kamloops. The Tertiary volcanic rocks between Vernon and Kamloops have been explored by rockhounds for semi-precious and decorative stones such as agate, chalcedony, amethyst and common opal throughout the last century. Significant interest was generated by the discovery of precious opal near McGregor Creek in 1991 followed by the development of the Klinker opal deposit (MINFILE 082LSW125) by Okanagan Opal Inc., 23 kilometres northwest of Vernon.

Regionally, the area is underlain by Upper Triassic to Lower Jurassic Nicola Group sedimentary and volcanic rocks that 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 and Penticton Group volcanic and sedimentary rocks overlie the older units.

Locally, a sequence of massive to columnar jointed basalt to andesite -basalt flows occur. These are medium to dark greys to green greys, and fine grained to aphanitic. Elongate, commonly aligned vesicles and amygdules up to several centimetres in length, some larger cavities are up to 20 centimetres long, are common in the host basalt.

Precious-common opal, agate-chalcedony and a variety of other white- to greenish- coloured minerals including clays and probable zeolites form space and fracturing fillings. The opal and agate often occur together, both filling primary cavites such as vesicles as well as fine fractures. Variably banded agates, up to 10 centimetres in diameter, have grey, white and clear bands with local semi transparent colourless and white opal bands and laminae. Transparent to opaque opals are common and precious opal occurs in a broad range of base colours including transparent, white, green, orange and browns. Precious opals display pinfire, mosaic (harlequin) and flash play-of-colour with variable brightness. Colours often include red, green and some blue, local violet (Assessment Report 27185).

In 2001, preliminary exploration for agate resulted in the discovery of common and precious opal (and agate) in float and bedrock basalt. Further opal discoveries were made, in 2002, along the cliff.

In 2003, prospecting and limited stripping of bedrock revealed common opal and local patches of precious opal in several areas proximal to the original discovery. These are spaced over a 150 metre length along the cliff.