The Paraguaçu rises in the Chapada Diamantina, the highland plateau that dominates central Bahia. Its water flows east toward the Bay of All Saints, cutting through sandstone and quartzite whose geology in places produces alluvial diamonds - stones washed out of their original matrix and deposited in gravel bars along the river. The Sincura range follows the Paraguaçu's course. When prospectors found stones along the river in the 1830s, the resulting camps bore the names of the villages nearest to their diggings: Paraguaçu, Combucas, Chique-Chique, Causu-Boa, Andraí, Nagé, and Lançois. Lançois - twenty leagues from Paraguaçu, by the account of the 1840s correspondent - held 3,000 houses and 20,000 inhabitants. Paraguaçu, the commercial hub where the miners went on weekends to sell their stones for Brazilian paper money, had only twelve small masonry houses and a population that still crowded in anyway.

The diamonds of Sincura were not uniformly prized. Stones from Paraguaçu, the correspondent wrote, were mostly "of a dun colour and very irregular conformation" - the kind of diamond that worked for industrial or low-grade jewelry use but not the high-grade market. The stones from Lançois were different. White or light green, "nearly transparent as they come from the mine," and octahedral - shaped in the natural crystalline form that meant a cutter could work with them directly. Those diamonds were the most valuable. Miners dug three or four yards into the gravel to reach the diamond-bearing stratum, or they gathered them from the stony ravines at the bottom of the Paraguaçu itself. Everything that came out of the pit had to be walked back to Paraguaçu on a Saturday or Sunday and exchanged for the manufactured goods - arms, clothing, flour, salt - shipped inland at great cost from Salvador on the coast.

The Bahian diamond rush eventually faded, outcompeted by the South African fields in the 1870s and 1880s. What is left today is harder to see from above. Some of the mining villages are still there - Mucugê, Lençóis, Andaraí, Igatu - folded into the Chapada Diamantina National Park, which was created in 1985 to protect the highlands where the Paraguaçu rises and some of the finest hiking country in Brazil. Their cobbled streets, colonial houses, and church façades are the direct architectural inheritance of the diamond money. Lençóis, population around 10,000 now, is a UNESCO-style tourist town, the kind of place where a gem dealer's counter sometimes sits next to a café. The Sincura range itself remains rugged and mostly uninhabited - a mountain chain whose most remarkable feature may be the one that the Latin dictionary entry tacked onto the end of the Wikipedia article quietly points at: sine cura, "without care." A place remote enough to sound like its own name.