Radiocarbon 14C Dating of hydrothermal siliceous sinter deposits from El Tatio Geyser field in the Chilean Altiplano. All samples were analyzed at the Keck-Carbon Cycle accelerator mass spectrometry laboratory (KCCAMS) at the University of California, Irvine. Radiocarbon concentrations are given as fractions of the Modern standard, D14C, and conventional radiocarbon age, following the conventions of Stuiver and Polach (Radiocarbon, v. 19, p.355, 1977). Sample preparation backgrounds have been subtracted, based on measurements of 14C-free wood. All results have been corrected for isotopic fractionation according to the conventions of Stuiver and Polach (1977), with d13C values measured on prepared graphite using the AMS spectrometer. These can differ from d13C of the original material, if fractionation occurred during sample graphitization or the AMS measurement.