Many American states use the labor of inmates to help fight its fires, but none so more than California. Using incarcerated firefighters saves the state’s taxpayers an estimated $100 million a year.

The women that choose to enter the firefighting camps are afforded better pay, by prison standards, and an improved quality of time served. However, the money they earn from putting their lives on the line is dwarfed by the salaries of the civilian firefighters they work alongside — one woman reports to earn $500 a year, compared with the $40,000 starting salary on the outside.

On today’s episode of The Sunday Read, Jaime Lowe explores California’s invisible line of defense against wildfires.

This story was written by Jaime Lowe and recorded by Audm. To hear more audio stories from publishers like The New York Times, download Audm for iPhone or Android.