Acopinalco del Peñón

Acopinalco del Peñón is a village in the municipality of Tlaxco, in northern Tlaxcala, at about 2,642 metres above sea level. At the 2020 census it had 2,502 residents, up from 2,382 in 2010, and its founding is dated to 19 May 1920. The name is Nahuatl and is read as "on the other side of the water", from atl (water), copona (to draw out), nalli (the other side) and the locative suffix co.

What gives it the second half of its name is the rock: the Peñón del Rosario, also called cerro El Rosario, a massif of volcanic tuff crowned by a rock outcrop that can be seen from the village and from the road. It is the second-highest point of the Sierra de Tlaxco after the Huilacapitzo (about 3,500 m) and reaches roughly 3,440 metres by most accounts (another figure is 3,404). Its north, south and east faces are almost vertical, and the north slope is covered in dense pine, juniper and oyamel forest.

On the west side the approach is gentler: a logging track leaves from Acopinalco and El Rosario, and a staircase eases the last stretch to the top. The climate is temperate and subhumid, with an average of about 14 °C a year and 600 to 700 mm of rain, almost all of it from June to October. The summit sits right on the state line and INEGI places it on the Puebla side (Chignahuapan), so the village and the southern slope are in Tlaxcala.