40Ar/39Ar dating indicates that the youngest eruptions at the Valles caldera occurred at 74.4 ± 1.3 ka and 68.3 ± 1.5 ka.
U/Th dating of zircon crystal faces indicates protracted magmatism extending from the eruption age to at least 350 ka.
The extended period of zircon crystallization documents a previously unknown pulse of magmatism at the Valles caldera.
Combining these two dating methods will be useful for understanding the volcanic history of other late Quaternary systesm.