Final answer:
The term that best defines people who sought riches in California in the mid-1800's is forty-niners.
Step-by-step explanation:
The term that best defines people who sought riches in California in the mid-1800's is forty-niners. In 1848, gold was discovered in California, leading to a massive influx of people, known as 'forty-niners,' who came from all over the world in search of wealth and opportunities. These individuals played a crucial role in the California Gold Rush and the development of the state.
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