The Harnai route, although longer, is the one adopted for all ordinary traffic, the Bolan loop being reserved for emergencies. At the Khundilani gorge of the Bolan route conglomerate cliffs, which rise to a height of 800 ft., enclose the valley. At Siri Bolan the passage between the limestone rocks hardly admits of three persons riding abreast. The temperature of the pass in summer is very high, whereas in winter, near its head, the cold is extreme, and the ice-cold wind rushing down the narrow outlet becomes destructive to life. Since 1877, when the Quetta agency was founded, the pass was secured by the British Indian Army from militias of Baloch tribesmen (chiefly Marris). See also Balochistan Kacchi Plain Mehrgarh Sulaiman Mountains References Geography of Pakistan Mountain passes of Balochistan (Pakistan) Mountain passes of Pakistan