Devils Tower National Monument was established in 1906 and is comprised of 1,347 acres in Crook County, Wyoming. It is located in northeastern Wyoming on the northwest edge of the Black Hills. The 867 foot high Devils Tower was formed by the intrusion of igneous material into softer sedimentary rocks which later eroded to expose the tower. It attracts thousands of climbers each year. Ponderosa pine forests/woodlands cover approximately 60% of the monument. Six types of prairie grasslands occupy roughly 30% of the area in small patches within the more dominant ponderosa pine forest and woodland. The Belle Fourche River flows through the eastern part of Devils Tower NM and forms part of its southern boundary. Deciduous forests/woodlands (including plains cottonwood riparian woodland) occur in about 5% of the monument. Early efforts to document the Monument’s flora included significant contributions by Laura Joyner, wife of an early superintendent, and George W. Giles, working for the Works Project Administration. The first comprehensive plant species inventory was carried out in 1981-1982 (H. Marriott). An extensive list of plant species for Devils Tower NM was reviewed and certified by Marriott in 2004. Ten additional species were found in a survey for plant species of concern in 2008 (B. Heidel) and additional information relevant to the status of several other species has been generated in recent years. The Monument's certified plant list currently is being updated, through fieldwork and review of secondary sources. It is estimated that the known flora contains on the order of 460 species. At this time, there are 800 plant specimens in Devils Tower NM herbarium which is housed at Mount Rushmore National Memorial museum.