Tonopah is a census-designated place 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 power producer in the country, nuclear or otherwise.It is located on the Tonopah Desert. Many wells in Tonopah are warm, in the 70 to 95 degrees F range and many are hot; 110 to 120F wells are common. Prior to being called Tonopah, the settlement was known as Lone Peak.The area is also known to have been inhabited by groups of people for resource gathering area of the Hohokom, Patayan and Yavapai.