Forgotten Tragedy: The Story of the St. Francis Dam tells the tale of the largest man-made disaster of the 20th century. This tragedy has now been largely lost to history. This movie is a journey through the early history of Los Angeles and the city's water needs. This ever growing demand led to larger and larger projects, and eventually to tragedy. The film discusses the history of the tragedy, the roll of William Mulholland in the disaster and the city's water development, and how the lessons of the tragedy reflect on our current infrastructure needs today.