This is a Federal Register notice of a preliminary permit application filed by Twentymile Pumped Storage, LLC (docket P-15305-000) with FERC for the Twentymile Pumped Storage Project near Oak Creek in Routt County, Colorado. The project proposes an above-ground upper reservoir and an underground lower reservoir using sealed mine voids, connected by a penstock and underground powerhouse with 250 MW generating capacity and estimated annual generation of 547,500 MWh. A preliminary permit, if issued, grants only priority to file a license application; it does not authorize ground disturbance. Comments and competing applications are due 60 days from the notice's issuance.