Query: Where is Mount Tangjia?
Context: The most precarious of these quake-lakes was the one located in the extremely difficult terrain at Mount Tangjia in Beichuan County, Sichuan, accessible only by foot or air; an Mi-26T heavy lift helicopter belonging to the China Flying Dragon Special Aviation Company was used to bring heavy earthmoving tractors to the affected location. This operation was coupled with the work done by PLAAF Mi-17 helicopters bringing in PLA engineering corps, explosive specialists and other personnel to join 1,200 soldiers who arrived on site by foot.