Creosotebush (Larrea tridentata (DC.) Coville) aggressively invades desert plains grassland in Arizona, New Mexico, and western Texas. Gardner (10) recorded invasion of grassland along the Rio Grande Valley in southern New Mexico and pointed out that it takes the form of frontal advances along the margins of the larger creosotebush communities and of a single plants and then small outlier stands at varying distances from the main bodies of the larger communities. Yang (21) recorded invasions of grassland on upland plains adjacent to the Rio Grande Valley. Buffington and Herbel (2), using 1858 General Land Office survey records and recent observations, reported increase of creosotebush on the Jornada Experimental Range in southern New Mexico from 644 acres of moderately invaded range (creosotebush comprising 15 to 55 percent of the perennial vegetation) in 1858 to 12,388 acres of heavily invaded range (55 to 100 percent of vegetation) in 1963.