Hydraulic fracturing, or fracking -- using water, sand and chemicals at high-pressure to crack shale formations and release oil and gas -- is practiced in more than 30 states. But we’re still learning about how communities may be impacted by the practice.

Beneath the farms, orchards and vineyards of Central and Southern California lies a prehistoric soup worth a fortune. But new ways of extracting oil and gas have come with reports of air and water pollutions, as well as risks to public and environmental health. This has many in California concerned.