All of the responses highlight negative impacts of gold and silver mining in the West, but the most comprehensive answer would be:
Mining camps were sources of many contagious diseases.
This response addresses a significant health concern that arose due to the rapid influx of people into mining areas, resulting in overcrowded conditions that facilitated the spread of diseases. While other options also describe negative consequences, the mention of diseases emphasizes a public health impact that affected many individuals during the mining boom.