Soils derived from the Bear Den Member of the Eocene-age Golden Valley Formation in western North Dakota are of limited extent (approximately 30,000 hectares), but have unusual soil mineralogy, morphology, and chemical properties that make them unique in the northern Great Plains. Geologists report that these sediments have undergone more intensive and extended weathering than the sediments from surrounding geological materials. Soils formed in these materials from the Golden Valley Formation present special challenges for erosion and fertility management. To characterize these soils, the mineralogy and selected soil chemical and physical properties were evaluated and summarized. The data indicates that the dominant soils from this area would classify as Argiustolls or Haplustolls, with mixed mineralogy. However, the activity class is semi-active or active, and Cation Exchange Capacity (CEC) values are much lower than similar surrounding soils that developed from the other geological formations in this region. Organic carbon, pH, carbonates, and Coefficient of Linear Extensibility (COLE) values are also lower in these soils. The soils derived from the Bear Den Member of the Golden Valley Formation have unique characteristics and soil properties that make it necessary to correctly identify, classify, and delineate them in order to develop appropriate soil interpretations and management practices.