Abra del Acay is the highest point on Argentina's Ruta 40, at 4,895 metres, and one of the highest road crossings in the Americas. The pass lies in the province of Salta, on the road between San Antonio de los Cobres on the puna to the north and the village of Payogasta and the Calchaquí valley to the south. The rock around it is bare and fractured, the sky is a darker blue than you are used to, and on the horizon stands the snowy mass of Nevado del Acay, over five and a half thousand metres.
Altitude is the real subject here. A motorcycle makes noticeably less power at this height, and carburetted engines run rich and sluggish while fuel-injected ones cope better but still feel strangled. The rider is no better off: headaches, short breath and clumsy thinking are normal, and stopping for ten minutes at the top is an excuse rather than a hardship. Drink plenty, eat lightly and do not hang around for the sunset. Take the pass in the middle of the day, when the wind is lowest and the surface thawed, and watch for ice patches in the shadow of the corners, even in summer. Snow can shut the road in winter, and storms can arrive from nowhere.
The road is a work of patience. From San Antonio de los Cobres, a small mining and railway town on the high plateau, the surface is mostly paved for a stretch and then gives way to gravel, in tight hairpins on the descent toward Payogasta. Traffic is thin. You may meet a truck or a pickup and more often a herd of vicuñas, the slender wild relatives of the llama, or a guanaco standing on a ridge as if posted there. Check conditions in San Antonio before you start.
History lies close by. The ruins of Santa Rosa de Tastil, a large pre-Inca settlement of stone houses on the quebrada, are a short way along the main road to the north, and the old route here was a path for llama caravans long before motorcycles, linking the puna with the valleys below. Fuel is the practical question: San Antonio de los Cobres has a pump, but carry a spare bottle, because queues and shortages are not unknown. Cachí, further south, is the better-stocked place to refuel, and the descent there passes through some of the most dramatic colour on the whole route.