The border between the United States and Mexico stretches 3,145 kilometers (1,954 miles), from the Gulf of Mexico to the Pacific Ocean. In some places, the border is only marked by a sign or a fence. In other places, the border is reinforced with barbed wire or tall steel barriers.

One of the most strongly fortified areas of the border separates the urban areas of San Diego, in the U.S. state of California, and Tijuana, in the Mexican state of Baja California. Here, the border is marked with double and even triple fencing. The first fence, pictured above, is about 3 meters (10 feet) tall, and made of thick metal plates. The second fence, behind the first one, reaches 4.5 meters (15 feet). The top is angled inward, with barbed wire at the top. In some areas, there is a smaller chain-link fence behind the second one. In between the fences is "no-man's land," an area that the U.S. Border Patrol monitors with bright lights, armored trucks, and cameras.

All the border fortification is intended to reduce illegal immigration to the United States from Mexico. Most immigrants who cross the U.S.-Mexico border illegally flee extreme poverty in Mexico. Others have come through Mexico from Central and South America.

Crossing the border near Tijuana-San Diego is dangerous. The crosses in this photograph represent the hundreds of men, women, and children who have died in the area while trying to reach the United States.

Most immigrant deaths in the Tijuana-San Diego area are due to exposure. Exposure is simply being exposed to severe weather. The Sonoran Desert receives very little precipitation. It is very hot during the day, with few trees to provide shade. The desert is also very cold at night. Immigrants who are not prepared with adequate water, protection from the sun, and warm clothing are at risk for dehydration, heat stroke, or hypothermia.

The phrase "Ni Una Muerte Mas! Reforma Ya!" means "Not one more death! Reform now!" It is the slogan of Border Angels, a nonprofit organization focused on American immigration reform and reducing the number of immigrant deaths in the Tijuana-San Diego area.

adequate
Adjective

suitable or good enough.

barbed wire
Noun

twisted metal with sharpened points, often used for fences.

Noun

natural or artificial line separating two pieces of land.

dehydration
Noun

illness in which the body loses too much water.

fortify
Verb

to strengthen.

hypothermia
Noun

potentially deadly condition in which an organism's body temperature drops.

illegal immigrant
Noun

person who has migrated to a nation without following the immigration laws of that nation.

monitor
Verb

to observe and record behavior or data.

nonprofit organization
Noun

business that uses surplus funds to pursue its goals, not to make money.

poverty
Noun

status of having very little money or material goods.

Noun

all forms in which water falls to Earth from the atmosphere.

reinforcement
Noun

supplies or personnel provided as support.

steel
Noun

metal made of the elements iron and carbon.

Noun

developed, densely populated area where most inhabitants have nonagricultural jobs.

Noun

state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.