The Washington occurrence is located near the headwaters of the south fork of the Marmot River, 14 kilometres southeast of Stewart. The region is underlain by hornfelsed sediments and volcanics of the Middle-Upper Jurassic Salmon River and Lower Jurassic Unuk River formations (Hazelton Group). These are intruded to the southwest by granodiorite of the Eocene Hyder pluton (Coast Plutonic Complex).

The showing comprises four north striking, vertically dipping, subparallel shear zones 15 to 30 metres apart. These zones, up to 1.8 metres wide, occur in volcanic breccia and lithic tuff of the Unuk River Formation. The zones terminate against a northeast striking fault to the south. An adit, 120 metres long, driven 30 metres below the lowest exposed shear zone failed to intersect any of the shear zones, indicating that they may be cut off by faulting at shallow depths. The zones are mineralized with pyrite, galena, sphalerite and possibly tetrahedrite. Samples of high grade silver ore have been obtained from here (Minister of Mines Annual Report 1926, page 88).

Granby Gold Inc.'s Marmot property, containing the Washington showing, underwent geological mapping throughout 2013 to 2015. In 2017 the geology was finer tuned by interpretation with regional airborne geophysics and again in 2018 with airborne geophysical survey data.