The only river that partially forms the southern border of the U.S. is the Rio Grande on the Texas/Mexico border. The rest of America's souther border with Mexico is a land border in souther New Mexico, Arizona, & Colorado.
Yes. New Mexico's southern border touches the border of Mexico. A couple of New Mexico cities that are close to the Mexican border include Chaparral, NM & Columbus, NM. Glad to help! Regards, Ryan S. :)
Both are equally right; however, Southern Mexico is a specific region encompassing three states: Oaxaca, Guerrero and Chiapas; southern Mexico is a more general area that could be anywhere south of Mexico City, down to the border with Guatemala and Belize.