Sasabe is a border town in Mexico where many undocumented migrants begin their journey.

Many undocumented migrants traverse the vast and uninhabited Sonora Desert in hopes of crossing through undetected. To travel north through Cabeza Prieta National Wildlife Refuge, undocumented migrants follow a guide.

Migrants often mark the location of a camp with bandanas, water jugs or in this case the popular energy drink Red Bull. A marker also may indicate the location of a migrant's death.

Undocumented migrants often build shelters that blend into the landscape to shield them from the sun and avoid detection by Border Patrol helicopter patrols.

Undocumented migrants often pass through protected areas like the San Pedro Riparian Conservation Area in eastern Arizona.

According to recent Tohono O'odham lore, a local woman saw the Virgin of Guadalupe in this sahuaro crowned with the white blossoms of summer. The cactus quickly became a shrine. Undocumented migrants regularly visit the shrine.

Sacred to the Tohono O'Odham nation, Baboquivari Mountain serves as an important landmark for undocumented migrants as they pass through the Altar Valley on the east side of the Baboquivari range.

This shrine is set in a canyon wall along a frequently used migrant trail. Migrants adorn the shrine with photographs of their loved ones and prayer cards featuring the patron saint of their homeland.

Along with coins, matches, candles, prayer cards, family photographs, scapularios, migrants leave cards featuring the patron saint of their homeland. Seen here are the Virgin of Guadalupe (important throughout Mexico), the Virgin of Juquila (worshiped in Oaxaca), the Virgin of San Juan de los Lagos (worshiped in Jalisco) and Toribio Romo (a priest who was martyred during the Mexican Revolution and regularly appears to distressed migrants in the desert).

The figure of the Virgin of Guadalupe, also called the Patroness of the Americas is featured on many objects migrants take on their journeys, from prayer cards, bandanas, to t-shirts.

This shrine appeared in 2006 at a rest stop along a heavily used migrant trail about 30 miles north of the U.S. border. That undocumented migrants carry prayer candles such great distances is a testament to their faith.

Water is heavy and undocumented migrants often find creative ways of easing their load. The drying sour melons signal the end of the summer rains.

If U.S. Border Patrol agents apprehend undocumented migrants, they are turned over to Wackenhut, a private contractor who transports them to a detention center for processing. Migrants often await transport for long hours without food and water.

Children often make the journey north with family or to reunite with parents.

This sweatshirt is wrapped around a vehicle barrier post that forms the southern boundary of the Tohono O'odham nation in the United States.

Women's undergarments in trees may indicate sites where migrant women have been raped.

Jesús Malverde is the patron saint of narco-traffickers.

This shrine is located near a pickup site deep in the Sierrita Mountains.