Prismas Basálticos

The Prismas Basálticos of Santa María Regla line the walls of a narrow ravine about 6 kilometres from Huasca de Ocampo and 38 kilometres from Pachuca. They are columns of basalt, mostly five- and six-sided, about 80 centimetres across and up to 30 or 40 metres tall, standing upright in some places and stacked sideways in others. They formed about 2.5 million years ago, when a thick lava flow ran into a body of water: the stream flowing over the top cooled the lava slowly and evenly, and as it shrank it cracked into polygons with three to eight sides. The San Antonio Regla river, held back upstream by the San Antonio dam, pours over the columns in four waterfalls, the last of them called the Cascada de la Rosa. In the 19th century the whole spot was known simply as the Cascada de Regla.

The ravine sits among the silver haciendas that Pedro Romero de Terreros, later the Count of Regla, built along the river between 1760 and 1762 to refine ore from Real del Monte. It has drawn scientists and artists ever since: José Gutiérrez sketched it for the Malaspina expedition in 1791, Alexander von Humboldt drew the "basalt rocks and waterfall of Regla" on 21 May 1803, in the first published geological account of the columns, and Johann Moritz Rugendas painted it in 1832. Today it is one of the sites of the Comarca Minera UNESCO Global Geopark.

The site is a developed ecotourism park rather than wild nature. Stairs, walkways and hanging bridges take you down to the foot of the falls and across the canyon for views of the columns from above. The entry ticket also covers the viewpoints, pools and picnic grills, while the zip line, camping, cabins and horse rides are paid separately. Upstream, the San Antonio Regla dam offers boat and horse rides.