Tonopah is an unincorporated community in western Maricopa County, Arizona, United States, approximately 50 miles west of downtown Phoenix off Interstate 10. The community is near the Palo Verde Nuclear Generating Station, the largest nuclear power plant in the country. The name Tonopah derives from the Western Apache Tú Nohwá, meaning "Water Under a Bush", referring to its location in the Harquahala Valley, underneath which there is an extensive subterranean aquifer so that wells dug in the area never lack water. Prior to being called Tonopah, the settlement was known as Lone Peak. The area is also known to have been inhabited by the Yavapai.