In an action challenging a ballot initiative ordinance prohibiting the growth, testing, and cultivation of genetically engineered crops until the County conducted an environmental and health impact study, the District Court's denials of appellants' motions to intervene are affirmed where: 1) prospective intervenors are not 'parties' for purposes of section 636(c)(1); and 2) a magistrate judge who has the consent of the named parties to the suit may rule on a prospective intervenor's motion to intervene without the prospective intervenor’s consent.