The major desert located in the Southwestern United States is the Sonoran Desert. Spanning parts of Arizona, California, and Mexico, it covers around 100,000 square miles. The Sonoran Desert is known for its unique biodiversity, including iconic plants like the saguaro cactus, and various animal species adapted to its arid environment. Its climate is characterized by hot summers and mild winters, with a significant amount of rainfall during the summer monsoon season. This desert is also home to vibrant ecosystems and serves as an important area for research and conservation.