MEMORANDUM **

Two individuals formerly employed as fire lookouts, and members of their families, appeal pro se from the district court’s judgment in their action claiming that defendants caused them to be exposed to electromagnetic radiation in excess of federally-permissible limits and thereby vio *639 lated 47 U.S.C. § 206 and California state law. We have jurisdiction under 28 U.S.C. § 1291. We review de novo. Proctor v. Vishay Intertechnology, Inc., 584 F.3d 1208, 1218 (9th Cir. 2009). We affirm.

The district court dismissed the plaintiffs’ claim of strict liability based on ultra-hazardous activity. By failing to raise any arguments in their opening brief addressing the district court’s ruling on this claim, the plaintiffs waived this challenge. See Smith v. Marsh, 194 F.3d 1045, 1052 (9th Cir. 1999).

The district court properly granted summary judgment on the claims of negligence per se and violation of 47 U.S.C. § 206. Those claims were litigated and decided in an earlier state court action brought by some of the plaintiffs here (with whom the remainder are in privity). See Jasso v. Cal. Dep’t of Forestry, Superior Court of California, County of Lassen No. 41697; see also First Nat’l Bank v. Russell (In re Russell), 76 F.3d 242, 244-45 (9th Cir. 1996) (describing the elements of collateral estoppel under California law to be: (1) the issue decided in the earlier ease is identical to the issue presented, (2) the earlier case culminated in a final judgment on the merits, and (3) the party against whom estoppel is asserted was a party to, or was in privity with a party to, the earlier case).

AFFIRMED.