Tracey Bratt-Smith knows exactly how far away from home she needs to search — 2 1/2 miles.

That, Bratt-Smith has learned, is usually the radius people travel before they die by suicide. She believes if searchers stay within that distance from her home in St. George, they will find her son, Macin Smith.

“We’ve done many searches around the perimeter," Bratt-Smith said, "but there’s so much desert area and rock cliffs and terrain that we’ve never meticulously looked in.”

Smith disappeared at age 17. On Saturday, his family is organizing a search to find him on the eastern outskirts of St. George.

The search will begin 8 a.m. Saturday at 3000 E. Banded Hills Drive. The Smith family especially wants people with ATVs or horses to volunteer.

Smith is the youngest of six children. His mother, in a telephone interview Monday, said her older children were raised in Saratoga Springs. Smith, she said, suffered from depression, and one reason the family moved to St. George was for the sunlight and better weather.

Bratt-Smith said her youngest son was doing well at St. George’s Desert Hills High School. Then on Sept. 1, 2015, he didn’t come home. His family later found his wallet with a note inside. Bratt-Smith declined to specify what it said except to say he intended to hurt himself.

“He basically indicated he was broken and had been for years," Bratt-Smith said.

Local police investigated the disappearance and looked for Smith in the early weeks before concluding it was a suicide, Bratt-Smith said.

The Smiths live in the last subdivision before St. George Regional Airport. There is a valley nearby with red rock desert and sagebrush.

Bratt-Smith expects 150 volunteers to help search Saturday. Anyone interested in participating can learn more at a Facebook page dedicated to the search. Go to Facebook.com and search for “MacinsArmy.”