If the Glen Canyon Dam was to somehow fail i.e. in a earthquake or terrorist attack, then a vast area of the Southwestern United States of America would basically become uninhabitable for about 2o years.

The economic and financial problems it would create would also bankrupt all the western financial institutions i.e. wall street due their exposure to the collapse of property prices in the south western USA where a huge proportion of the 2000-2008 property speculative bubble was generated.