What did the ringing of bells throughout the US's National Park Service areas on 19 August 2019 mark?

Question

Which noted waterfall falls from the edge of the Auyán-tepui mountain in the Canaima National Park, a UNESCO World Heritage site in the Gran Sabana region of Bolívar State in Venezuela?

Answer 1

The 400th anniversary of the landing of Africans traded as slaves in English-occupied North America
The landing was at Point Comfort in Hampton, Virginia, and the location is now part of the Fort Monroe National Monument, a unit of the National Park system. The Act which established the Service was passed in 1916.