The area of the Defries occurrence is underlain by Permian to Jurassic rocks of the Hozameen Complex comprised mainly of basalt, chert and pelite. These rocks have undergone regional, low grade greenschist facies metamorphism and generally contain fine-grained actinolite, epidote and chlorite.

In 1923, a large body of sulphide ore comprising chalcopyrite and sphalerite was reported. The property is described as being about 16 kilometres down the Skagit River from the 23 Mile Camp, in the area of Steamboat (Shawatum) Mountain.