 Mining revived in the early 1930s in response to the increase in the price of gold from $20 to $35 per ounce, but then virtually shut down during World War II when gold mining was declared nonessential to the war effort.The district was enlivened in the 1950s by efforts to locate uranium deposits, but these proved unsuccessful.The population of Central City and its sister city Black Hawk fell to a few hundred by the 1950s.