The correct answer to this open question is the following.
Although there are no options attached we can say the following.
The most famous and probably first "boomtown" in American history. Ships were abandoned in the famous harbor as people rushed to the hills to strike it rich.
Here we are talking about San Francisco, California, during the Gold Rush.
The California gold rush transformed the west of the United States.
The arrival of so many people that dreamt to find god a became rich, made possible the transformation of a region that before the gold rush, it was isolated with very few people and houses in that territory. But During and after the gold rush, the place changed completely because thousands of people settle in and formed new communities. Without a doubt, the massive migration changed the way that the place looked.
All this movement of goods and people during the Gold Rush in the 1860s made the city of San Franciso exponentially grow. The mass migration of the so-called Forty-niners changed the city of San Francisco and made it an important commercial hub that impulsed the economy of the area.