24 C.F.R. § 58.14
A responsible entity shall consult with appropriate environmental agencies, State, Federal and non-Federal entities and the public in the preparation of an EIS, EA or other environmental reviews undertaken under the related laws and authorities cited in § 58.5 and § 58.6 . The responsible entity must also cooperate with other agencies to reduce duplication between NEPA and comparable environmental review requirements of the State (see 40 CFR 1506.2 (b) and (c) ). The responsible entity must prepare its EAs and EISs so that they comply with the environmental review requirements of both Federal and State laws unless otherwise specified or provided by law. State, Federal and local agencies may participate or act in a joint lead or cooperating agency capacity in the preparation of joint EISs or joint environmental assessments (see 40 CFR 1501.5(b) and 1501.6 ). A single EIS or EA may be prepared and adopted by multiple users to the extent that the review addresses the relevant environmental issues and there is a written agreement between the cooperating agencies which sets forth the coordinated and overall responsibilities.
24 C.F.R. §58.14