(Photo courtesy of Migrant Trail Facebook group)

Participants walk 75 miles from the Mexico border to Tucson over the course of one week.

In recent years, thousands of immigrants have died while trying to cross the U.S.-Mexico border. An annual pilgrimage in Arizona aimed at drawing attention to their plight began Monday morning.

A coalition of groups organized the 13th annual Migrant Trail. They set off from Sasabe, Mexico, this morning and are due in Tucson on June 5th

Participants came from as far away as Central America to walk 75 miles from the border to Tucson over the course of one week. Organizers say they expect 150 people to make the journey, calling attention to the more than over 6,000 people who have died while crossing the U.S.-Mexico border since the 1990s.

The U.S. Border Patrol reported 240 migrant deaths in fiscal year 2015, a decrease from 2014.

Advocates say many more migrants who die are never found.