The 70th Hunger Games was the Hunger Games that took place four years prior to the start of the series. This Hunger Games was won by Annie Cresta, the female District 4 tribute. These Games are mentioned in Catching Fire, though little is known about them.
It was stated by the Gamemakers that only a few tributes had died after a few days of the games. According to the Gamemakers, the games had "become a little boring," since only a few people were dead. In response to this problem, the Gamemakers started an earthquake to break a dam overlooking the arena. The dam's collapse produced a massive flood that flooded the entire arena, drowning most of the tributes.
Being from the fishing district, Annie Cresta was the strongest swimmer in the Games, and was thus the only survivor of the flood, securing her as victor of the 70th Hunger Games.