 In the southern and western parts of the county, the volcanic cliffs of the Candelaria Rimrock (also called the Sierra Vieja) rise perpendicular and run parallel to the river, separating the highland prairies from the desert floor hundreds of feet below them.The gravel pediment, which allows only the growth of desert shrubs and cacti, extends from the Rimrock to the flood plain of the river.Along the river, irrigation allows the farming of vegetables, grains, and cotton.