Cal. Pub. Res. Code § 3739

Any person engaged in operating any wells wherein high pressures are known to exist, and any person drilling for geothermal resources in any district where the pressures are unknown shall equip the well with casings of sufficient strength, and with such other safety devices as may be necessary, in accordance with methods approved by the supervisor, and shall use every reasonable effort and endeavor effectually to prevent blowouts, explosions, and fires.