During Gold Rush events, you are awarded Gold for destroying Crown Towers in 1v1 Arena battles. The first Princess Tower you destroy gives a certain amount of Gold (say n) depending on Arena level, the second Princess Tower gives 1.5n Gold and the King's Tower gives 2n Gold. You can get at most 25n Gold during each Event. The Crown Towers are also decorated with gold.
During Gem Rush events, you are awarded Gems for destroying Crown Towers. The Crown Towers are also decorated with gems. The rewards are the same at all Arenas.
Introduced in the October 2017 Update. There have been 9 Gold Rush Events and 3 Gem Rush Events so far.
The December 2017 Update added one Arena and raised the maximum Gold in Gold Rush Events from 5,000 to 6,000.
The June 2018 Update improved the Gold economy and raised the maximum Gold in Gold Rush Events from 6,000 to 10,000.
During some of the events, you get a Quest that is completed by gaining 10 Crowns in 1v1 Arena battles. This Quest can be easily completed together with a Crown Chest.