The Rio Grande showing is on the west bank of the Tulameen River, 250 metres north of the river's confluence with Podunk Creek and 32.5 kilometres west-southwest of Princeton.

The area is underlain by biotite granodiorite of the Late Jurassic to Early Cretaceous Eagle Plutonic Complex. To the west, calc-alkaline volcanic rocks of the Late Oligocene to Early Miocene Coquihalla Formation outcrop.

Locally, a shear zone, 1.5 metres wide, is developed in granodiorite in the western margin of the Eagle Plutonic Complex. The zone contains narrow stringers of massive galena and sphalerite, 2.5 to 10 centimetres wide, in a sheared matrix of kaolin, sericite, crushed quartz and oxidized pyrite.

A chip sample taken across the zone assayed trace gold, 14 grams per tonne silver and 1.2 per cent zinc, while a selected sample of galena assayed 0.7 gram per tonne gold, 463 grams per tonne silver, 28 per cent lead and 2 per cent zinc (Minister of Mines Annual Report 1928, page 267).

In 1990, a rock sample (44059) of andesite hosting quartz veins with greater than 2 per cent pyrite from the south side of Podunk Creek yielded 0.114 per cent copper (Assessment Report 20350).

The claims were originally staked in the winter of 1926. In 1990, the area was prospected as the Aur I-II claims by Athlone Resources.