Lesley Ann Warren and Sally Ann Howes turned down the role of Elizabeth. Kim Novak was also approached, and Diana Rigg was set to star as Elizabeth but was forced to withdraw due to illness.
Lee Marvin (Ben Rumson) drinks real alcohol throughout the picture even though the director fought him about it. In most pictures the actors drink tea for whiskey and water for vodka. Marvin would only work if he got real liquor.
When the town falls apart due to the tunnels collapsing, the smooth sides of the concrete tunnel are visible after the thin layer of mud falls down into them.
While working in the "mine", Ben Rumson can clearly be seen wearing a carbide lamp. Carbide lamps were not developed until 1892, but the movie is set in 1849.