Eric Gray, a trails maintenance worker at the Grand Canyon, leads a group of mules carrying supplies down a popular park trail, Tuesday, April 28, 2009 in the Grand Canyon National Park. The Grand Canyon lures millions of people each year with its colorful landscape, immense size, and awe-inspiring geology. But it presents obstacles that can leave even experienced hikers emerging sore and fatigued during the scorching heat of the summer months, an altitude of 7,000 feet, and steep, rocky, winding trails. (AP Photo/Felicia Fonseca)