Yumen (yü-mŭn) [key], city, NW Gansu prov., China. It was long one of China's leading petroleum centers, with oil fields and refineries, but output has steadily declined since the 1960s. Yumen, on the Old Silk Road to Xinjiang, is named for an ancient gateway in the nearby Great Wall. It is on the railroad that connects Lanzhou and Xinjiang.
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