The Lumsden showing is located 3 kilometres west of Armstrong, at the base of Mount Rose.

In this area, sedimentary and volcanic rocks of the Upper Triassic to Lower Jurassic Nicola Group are in fault contact to the north with Cambrian-Ordovician volcanic (Tsalkom Formation) and sedimentary (Sicamous Formation) rocks. To the south the Nicola Group is in probable unconformable contact with Devonian to Triassic sedimentary and volcanic rocks of the Harper Ranch Group. Cretaceous granodiorite plugs of the Salmon Arm Intrusions intrude the Nicola, Sicamous and Tsalkom rocks. Outliers of Eocene Kamloops Group volcanic rocks are present in the area.

Cretaceous granodiorite has been quarried for industrial use. The granodiorite contains amber-coloured mica, has good rift and grain, and works with ease. However, the pyrite content makes it a poor building material.

About 1910 the stone was quarried for monument bases and building stone.