September 7 is the anniversary of the day that The Hoover Dam Begins Operations in 1936. The dam would take months to become fully operational, and still continues to this day. It's well known that the Dam would not have been built today, due to the massive ecological impact, as well as worker safety laws (100 - 200 people were killed during construction) driving up the cost of the project.
The ecological impact was massive. The Colorado River was historically a fertile land, ending in a vast wetland at the delta. The native tribes of the area relied upon it to provide for their needs. With the construction of the Hoover Dam, vast amounts of land upriver were flooded, and the rich wetlands at the delta are slowly drying up. To make matters worse, industrial pollution and irrigation have increased the salinity of the water greatly. When Lake Mead dries up (which is looking more and more likely), all that will be left is a barren wasteland. The way of life that served the first nations of the area is gone forever already. The US Supreme Court also very recently ruled that the US had no obligation to provide water to the Navajo people.
Honourable Mentions:
Matthews and Collett are permanently banned from the Olympics in 1972 by the American IOC President “Slavery Avery” Brundage. Their crime? Standing together on the first place podium and disregarding the US anthem. Slavery Avery was absolutely amazingly American.
Maryland and DC Schools Desegregrate in 1954. As expected, white students left public schools in droves, as they and their parents couldn't stand the thought of them standing aside black kids.