Cerro Porquesa

[1] The Quebrada de Piga, which flows to Salar del Huasco, originates at Cerro Porquesa.

[3] Another 0.28 mya old ignimbrite was originally attributed to Porquesa but instead comes from a 4 kilometres (2.5 mi) wide caldera in Bolivia.

In this gap volcanic activity younger than 2 mya isn't found and where lead (Pb) isotope ratios in rocks change with the radiogenicity of the isotope ratio decreasing northward.

The lower ratio was principally imparted by the low-radiogenic Pb upper crust.

[4] Samples and the appearance of the domes in aerial photographs indicate a homogeneous composition with about 68% SiO2.