Beyond Cachi the road passes through Payogasta, where the pavement that continues east toward Salta via the Cuesta del Obispo is left behind, and Ruta 40 turns north onto its high-altitude gravel alignment. The road follows the upper Calchaquí valley toward La Poma, a small village rebuilt a kilometre from its original site after a 1930 earthquake levelled the town — the ruins of La Poma Vieja, including the old church, still stand nearby as a quiet record of what was lost. La Poma sits at the edge of serious geology: seven kilometres south, the Puente del Diablo is a natural cavern carved through solidified lava from an ancient eruption, its interior strung with stalactites and stalagmites — a genuinely remarkable place, though one that requires a guide, specialist equipment, and several hours, and is best attempted outside the current itinerary.
Lunch in La Poma is the last easy stop before the crossing proper begins — trout from the glacial meltwater of the Acay is the dish this valley is known for, and a quiet, unhurried meal here is the right preparation for what comes next.
A short distance north of La Poma, the road begins its final ascent toward the Abra del Acay, which at 4,895 metres is the highest point anywhere on Ruta 40's more than 5,000 kilometres, and one of the highest paved-or-gravel road passes in the world accessible by ordinary vehicle. The climb is gradual but relentless, the vegetation thinning to nothing as the road gains altitude, guanacos and vicuñas sometimes visible grazing on what little grows this high. At the summit, a stone apacheta — an offering cairn built up over generations by travellers exchanging goods between the puna and the valley below — marks the traditional crossing point between two distinct worlds: the fertile Calchaquí Valleys behind, and the vast, arid altiplano ahead.
The road drops from the Acay onto the puna proper, a landscape of extraordinary scale and emptiness — flat basins ringed by volcanic peaks, the light hard and clear at this altitude, colour draining from the landscape until it reads almost entirely in ochre, grey, and the deep blue of the sky. The final approach to San Antonio de los Cobres runs along a short paved stretch into town.
At 3,775 metres, San Antonio de los Cobres is one of the highest towns in Argentina — a dusty, functional settlement in the middle of the Salta puna, its houses painted in cheerful colours that stand out against the surrounding ochre emptiness. The town's modern identity is bound up with the railway: built in the early 20th century as part of the Ferrocarril General Belgrano's push toward the Chilean border, it became famous as the starting point of the Tren a las Nubes, the tourist train that climbs to the Viaducto La Polvorilla — a spectacular Eiffel-era steel structure that the road passes directly on tomorrow's route north, making today's stop in town enough on its own.
The evening is for settling in at altitude rather than pushing further. A walk through the artisan market gives a look at weavers working at their looms, and the modest Iglesia San Antonio de Padua, for which the town is named, anchors the main square. The Museo Regional Andino covers the history and material culture of the puna people who have lived at this altitude for longer than any road has existed. Take the evening slowly — sleep can be difficult at this elevation on the first night, and there is no reason to rush it.
Deleting this waypoint is permanent and cannot be undone.