A tornado struck a workers camp in North Dakota’s oil patch on Monday, injuring nine people — one critically — and destroying at least eight trailers where workers had been living, an emergency management official said. The twister touched down at around 7:50 p.m. at a camp about 5 miles south of Watford City, which is in the west of the state and about 30 miles southeast of Williston, the city at the heart of the state’s oil boom.