Good stamp. The deterioration of Sino-Soviet relations in the late 1950s and early 1960s resulted in tensions along the 4,380 km (2,738 mi) border between China and the Soviet Union. A particularly serious incident occurred in May, 1962, when 60,000 ethnic Uyghurs in China's Xinjiang Province crossed the frontier into the Soviet Union, fleeing the desperate economic conditions. Beijing immediately accused the Soviets of subverting the Uyghur population, a charge that was later supported by some Chinese historiography, though never independently verified.