Want this question answered?
That would be some 1,160 Km or 721 miles.
The four Southwestern state of the US that are all on the border of Mexico are Texas, California, New Mexico and Arizona. From West to East they would be; California, Arizona, New Mexico and Texas.
Depending on how you define Southwestern states, you have Arizona and New Mexico for certain. California and Texas can be added to your list if your definition is broad enough. All of these states border Mexico. None of the states on the Canadian border would be considered "southwetern".
There is a steel mesh along the 220 Kilometers (137 miles) of the California-Mexico border. If you mean Baja California, it would be the Gulf of California or Sea of Cortes, which separates the peninsula from the rest of Mexico.
The Annexation of Texas. Texas border conflicts. Mexico was virtually bankrupt. Mexico would not negotiate the sale of Alta California and Nuevo Mexico.
California, Arizona, New Mexico and Texas.
Starting with Washington, Oregon, California, Arizona, New Mexico, Texas, Louisiana, Mississippi, Alabama, and Florida. If you stop at the Mexican border then you end with Texas.
Type your answer here... California, Arizona, New Mexico, and Texas
The state of Baja California begins at the US-Mexico border near San Diego. It would be some 130 miles south-east of Los Angeles downtown.
There are many cities along the US-Mexico border that would qualify as "closest to Mexico". Those would be Brownsville, Laredo o El Paso in Texas or San Ysidro in California.
The Compromise of 1850
That would be Tijuana (population: 1,286,187), near the US border and close to San Diego, California.