The cause of the gold rush was the discovery of gold in California in 1848. What was an effect of the gold rush?

A. Societies in China, South Asia and parts of Africa started using shells as a form of money.
B. Some farmers started trading their bushels of corn for baskets of tomatoes as part of a barter system.
C. Thousands of Native Americans started businesses based on gold and became rich.
D.Thousands of settlers moved west, leading to the growth of cities like San Francisco.