John King knew his small town of Rockdale, Texas, had landed on the global crypto map when three Chinese bitcoin miners showed up at City Hall unannounced this summer. Then came the phone calls to the city’s Chamber of Commerce, from investors asking about power hookups, to connect mining equipment they planned to ship from China. None had ever stepped foot inside the rural West Texas community, with a population of roughly 5,600 people. “I didn’t have any inkling [about what was happening in China] until my first phone call,” King said. “But there are lots of smaller miners that...