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Abstract The El Tatio geothermal field in the Chilean Altiplano contains hydrothermal silica sinter deposits overlaying glacial and volcanic units, providing an opportunity to constrain the timing of deglaciation and volcanic activity in an area with sparse absolute chronologies. We obtained 51 new radiocarbon ages andδ¹³C values on the organic material trapped in these sinter deposits. Based on the δ¹³C values, we exclude 29 samples for possible contamination with bacterial mats that incorporate old carbon. We infer that hydrothermal activity initiated ~27 ka ago and has been nearly continuous ever since. The ages of the oldest sinter deposits coincide with ages of moraines that stabilized after the most recent deglaciation. Whereas late Pleistocene sinters are broadly distributed in the field, Holocene deposits are found around active hydrothermal features. Although recent volcanism is absent in the vicinity of El Tatio, persistent hydrothermal discharge implies a long‐lived magmatic heat source.