On a quiet day, September 22, 1938, as work on Fort Peck Dam neared completion, the upstream portion of the east end of the embankment gave way at 1:15 in the afternoon. The earth shook, dredge pipes and railroad tracks shifted and sank, and a massive section of the dam swung out into the pool like a great earthen gate hinged on the east abutment. Machinery and men were swallowed up as 5 million cubic yards of earth slid into the reservoir, becoming an island. Eight men lost their lives, and six are still buried in the dam. A board of inquiry later reported that the slide occurred because the shearing resistance of the weathered shale and bentonite seams in the foundation was insufficient to withstand such forces. Thirteen months later, on October 11, 1940, the last load of material finalized construction of the dam, topping it out at a height of 250 feet, and since completion Fort Peck Dam has proven to be a safe, stable, and reliable structure.