The term 'NEIGHBOR OF MEX' refers to the countries that border Mexico. These countries are Arizona (ARIZ), California (CAL), United States of America (USA) and Guatemala (GUAT). Arizona is a state in the United States, located in the southwestern region of the country. California is also a state in the United States, located in the western region of the country. The United States of America is a federal republic composed of 50 states and a federal district. Guatemala is a country located in Central America.