Grasslands cover the eastern third of the Memorial, although some woody species such as desert broom and mesquite have invaded due to changes in the natural fire regime. The area north of the main park road is a mix of mostly native grass species while Lehmann lovegrass dominates much of the southeastern corner of the Memorial. This South African species was originally introduced in southern Arizona from the 1930's to the 1950's to prevent erosion, particularly along roadsides. It quickly adapted to the local climate and soils and spread rapidly to disturbed areas, especially where land had been degraded by overgrazing from cattle.