The 1970s were skateboardings renaissance, a skateboarding's golden age. 

The drought of 1976-1977 in California made swimming pools being emptied to conserve water which led to major pool skateboarding. It wasn't the only reason - brushfires, earthquakes and crack epidemic left homes abandoned with empty pools too. Skateboarders were jumping fences to ride in empty swimming pools. Before the drought skaters were using pools to skate but during the drought empty pools grew enormously and had major impact to the sports development - half-pipe, bowls and etc. 

Back then these guys were considered criminals although nowadays they are known as pioneers of skateboarding.