San Luis, Mexico, is not a border city. It is located approximately 186 kilometres (115 miles) south of the United States–Mexico border.
The nearest border cities are Tijuana and Mexicali, both in the state of Baja California. San Luis (likely referring to San Luis Río Colorado, Sonora, or San Luis Potosí city) is well inland. San Luis Río Colorado does sit on the border with Arizona, but the major city of San Luis Potosí is deep in central Mexico.