In a challenge to defendant-county's decision to issue a conditional use permit and mining permit, approve rezoning, to certify an environmental impact report (EIR), and to approve cancellation of a Williamson Act contract, dismissal of plaintiffs' petition for writ of mandate and complaint for injunctive declaratory relief is reversed where: 1) errors with the EIR analysis precluded "informed decision-making and informed public participation, thereby thwarting the statutory goals of the EIR process" and thus were prejudicial; 2) county failed to analyze the impacts of providing water to the proposed water system; and 3) county must do a water supply assessment or provide substantial evidence to explain why it did not have to comply with SB 610.