Phosphate mining was an important component of Granite County's economy from the 1940s through the 1960s. The mines were in Permian Phosphoria formation several miles up the Douglas Creek drainage near Hall. The geologic conditions are favorable as the formation is folded into an anticline and faulted so there several exposures of the main ore bed in a small area.
At first mining was conducted by the International Minerals and Chemical Corp. The phosphate rock is lower grade than the large mines near Garrison, and upgrading by flotation was necessary. The mill was next to the highway near the mouth of Douglas Creek. In the 1960s Cominco operated the mine with a mill part way between the mine and the highway. The spur to the mine and mill were named "Elephant" after Cominco's brand of phosphate fertilizer. Dave Harris worked in the mine for a time and says the mine was believed to have 40 years of reserves above the tunnel level. However after just a few years of operation the mine was shut and the mill equipment was moved to a Cominco mine in Greenland. According to Cominco's Montana manager, the mine simply could not match the costs of the big open pit phosphate mine at Vernal Utah. That mine is now owned by Simplot and is still operating.
Extensive records of the mine are located in the archives of the University of Montana. Environmental issues related to phosphate dust are discussed in some detail in the Clancy Gordon papers at UM.