Final answer:
The 49ers opposed slave labor in the California gold fields primarily due to economic competition, as it devalued their own labor and threatened their livelihoods. This led to resolutions and legislative efforts to ban slave labor. Option A is correct.
Step-by-step explanation:
The main reason 49ers were opposed to slave owners using slave labor in the gold fields was due to Economic competition. The influx of slave labor was perceived as a threat by white miners since slaves could be put to work without wages, undermining the efforts and potential earnings of the miners who did not own slaves. This economic self-interest galvanized the opposition to slavery in the California gold fields, leading to a push for rules and laws that would prohibit such practices.
White miners in California held a meeting to discuss this issue and resolved that “no slave or Negro should own claims or even work in the mines,” which was not long after followed by a delegate proposing a ban on slavery at the state constitutional convention. Such opposition was a combination of self-interested economic concerns and a desire to foster a society based on free labor, which they believed would be more industrious and offer opportunities for social mobility, in contrast to the slave-based economy of the South.