The calcareous soils in the San Bernardino National Forest host a group of endemic plant species, including five listed as federally endangered. The parent material for these soils is a very pure deposit of magnesium and calcium carbonate that is being actively mined. The mining operations produce copious quantities of dust. This study evaluated the quantity of dust moving across the landscape and depositing to the ecosystems, and the effect of carbonate dust on physiological parameters of a plant species acting as a surrogate for the endangered species. Most of the dust was found to deposit within one kilometer of the mining operations. Plants growing within the deposition zone had lower photosynthetic activity and less vigorous growth patterns. Several mitigation measures are recommended.