The California Gold Rush started when James Wilson Marshall was building a water-powered sawmill (for John Sutter) in 1848. When he finished building the mill, he went to the river to fetch some water. He saw some shiny little flakes of gold in the river. He immediately went to tell John, and they tried to keep it a secret. But word soon got out, and the gold rush started. It was 1849 when the Gold Rush started. People who came to California for gold were called forty-niners because they came in the year 1849. Some of them became rich but most did not.