A major invasion of grassland by shrubs began about 1850 A.D. in many desert areas of sourthern New Mexico. In the broad floor of the Jornada del Muerto Basin, mesquite (Prosopis glandulosa) is the most numerous of these invading shurbs. Mesquite roots in a coppice dunewere excavated and traced laterally in an area with an extremely complex soil pattern (Petrocalcids, Torripsamments, Haplargids, and Calciargids). The roots readily penetrated all soil horizons except the continuosly indurated petrocalcic horizon of the Petro clacids. However, the roots grew along the torp of the petrocalcic horizon and in places found locations for penetrationm such as cracks and pipes, with numerous, often upward-growing roots enrougte to utilize the sparse preciptation. At another study site mesquite encroached into a play dominated by Haplocalcids, in one of chich mesquite roots descended to a depth of at lease 5.5 m. Althoough thte spread of mesquite seed by cattle was a major factor in the spread of mesquite, its successful establishment over large areas was apparently due to the ability of mesquite roots to adapt to a wide variety of soils and soil conditions to take their advantage fo the sparse precipitation; to their ability to greatly proliferate while spreading laterally over long distances; to grow upward and take advantage of small precipitation events that only wet the soil to depths of a few centimeters; to descend to great depths along cracks and other openings in the soil, down which soil water also penetrates, and thus to their ability to utilize available water at all depths.