On September 22, 1938, at about 1:15 p.m., a vast section of Fort Peck Dam’s upstream embankment gave way. More than five million cubic yards of fill slid toward the rising Missouri reservoir. Eight workers died; six bodies were never recovered from the mass of earth.

The New Deal project—already the world’s largest hydraulic-fill dam—had employed more than ten thousand people at its peak. The slide did not destroy the works, but it forced a hard look at bentonite seams and shale beneath the structure and reshaped how the Corps finished the job.

Fort Peck still holds back one of America’s greatest reservoirs. The September failure remains a cautionary chapter in both Montana labor history and modern dam engineering.