The Calchaquíes are a branch of the Diaguita, and for more than a century they made this stretch of northwestern Argentina nearly ungovernable. The four Spanish towns founded between 1551 and 1630 each collapsed under sustained resistance. Even the Jesuit mission established here after 1637 was destroyed in 1660, during the last of the Calchaquí Wars. When the fighting finally ended, the Spanish crown did something brutal and decisive: it deported much of the valley's indigenous population hundreds of kilometers away, some as far as the outskirts of Buenos Aires. The valleys emptied. San Carlos grew slowly afterward, gathering around the rebuilt mission, a town founded as much on absence as on settlement.

By the early nineteenth century San Carlos had become the most important town in the Calchaquí Valleys, prosperous enough to imagine a grander future. When the question arose of which town should be the capital of Salta Province, San Carlos put itself forward - and lost to the city of Salta by a single vote. The independence wars left their mark too. In 1813, royalist officers under Pío Tristán sacked and burned the town to keep it from falling into patriot hands as the revolutionary army pressed north after the Battle of Tucumán. Within months the townspeople had thrown their support to independence, and in 1817 they supplied mules and horses to Gregorio Aráoz de Lamadrid's campaign into Upper Peru.

The ambition that nearly made San Carlos a capital is written into its church. Begun in 1801 on the site of an earlier private chapel and consecrated in 1854, the Church of San Carlos Borromeo is the largest in the Calchaquí Valleys and the only one built with both a transept and a dome. Its walls are thick adobe, raised by hand; its towers carry Europeanized flourishes that set it apart from the plainer chapels nearby. An earthquake in the 1930s shook the original vaulted roof so badly that it had to be replaced with wooden trusses and zinc sheeting, though the dome over the transept and apse, supported on rounded arches and timber beams, survived. Inside, the altars are dressed in the vivid folk imagery of the region.

Life in San Carlos still follows the rhythm of the valley. Artisans work in leather, ceramic, and woven cloth, and the surrounding vineyards yield the high-altitude wines the Calchaquí Valleys are known for, above all the fragrant white Torrontés. Each February the town gives itself over to a valley carnival of copleros - singers who trade improvised verses - while celebrants dust one another with flour and great bunches of basil. On the fourth of November, the feast of its patron, the image of San Carlos Borromeo is carried through the streets. A short walk out of town leads to Peñas Blancas, where an old indigenous cemetery lies, and to the poplar-lined waterfall at Celia's cascade.