Industrial mineral site no. 1834, known as "Sauk River Bridge Deposit" is a site in Skagit County, Washington. This site has been associated with limestone and marble. A notation found in DGER Bulletin 52 on page 303-304 says "Calcareous rocks of two types are exposed. One type consists of a bed about 4 feet thick of light-colored fissile thin-bedded calcareous shale, and underlying it is a 5 to 20 foot thick dark fine-grained carbonaceous massive calcareous shale", and designates the value as "The rock is too impure to be considered a limestone".