The Southwestern United States, also commonly called the American Southwest, is a region of the United States known for its many significant desert regions and the mountain ranges that divide them. Containing at its core the states of Arizona and New Mexico, the wider region within the United States is also usually associated with parts of California, Colorado, Nevada, Oklahoma, Texas and Utah, and the associated topographical features also stretch into parts of northern Mexico. In its various appearances in the Teenage Mutant Ninja Turtles multiverse, the Southwest is especially revered for its scenery, its spiritual significance and its connection with the supernatural.
In the Tales of the Teenage Mutant Ninja Turtles issue Swan Song of the Mirage continuity, an older Leonardo and his longtime human friend Raven Shadowheart (also known as Radical) tour the Southwest together. Radical is already familiar with the region as with many other places of open wilderness, as it puts distance between herself and the man-made building materials that are the domain of her nemesis Complete Carnage. But Leo is a newcomer to this land, and is so awed by its spiritual tranquility that his already perceptive spirit fully opens and bares itself to Radical's spirit. The two fully explore their love for each other in both mind and body, and continue to dwell together in the Southwestern wilderness for some time. But after this time together, during their first return visit to New York City, Radical is ambushed and killed on the sidewalk by Complete Carnage.
In the IDW miniseries Teenage Mutant Ninja Turtles: Casey & April, Casey Jones and April O'Neil drive April's van to California's Mojave Desert in the Southwest to search for leads on the Pantheon after the recently-murdered Professor Patrick Miller had shared his research notes with April. There, Casey and April are ensnared by the Rat King's trickery. But they also encounter the wise and kind goddess Aka who has made her home in the Southwest, and Aka informs April about the Pantheon, including the true nature of her sister goddess Kitsune.