AbstractAn examination of soil thermal and hydrologic regimes at several sites near Mayo, Yukon Territory, and the ground‐ice stratigraphy of a thaw‐slump headwall close to these sites supports the hypothesis that an ice‐rich zone, frequently observed at the base of the active layer, may be due to the annual water balance of permafrost. Observations demonstrate that ice lenses have grown at the top of permafrost in soil tubes installed in 1983. In addition, 90 cm of segregated ice are exposed in the thaw‐slump headwall above a thaw unconformity, dated at 8870 ± 200 years BP, but below the base of the present active layer. These data suggest that the rate of water incorporation into permafrost over the last 8000 years in the Mayo area has been at least 0.1