Samples were collected from four excavations and three muskegs for palynological examination in connection with a study of human prehistory in the Naknek drainage area, upper Alaska Peninsula. The purpose was to reconstruct the sequence of environments dating back to the earliest recognizable cultural phase, close to 4000 B.P. Pollen diagrams for muskeg show birch and alder as the principal arboreal types. Increasing percentages of alder occur during a late interval of hypsithermal time dating about 5500 B.P. Birch thereafter gained in proportion and between approximately 5000 and 2500 B.P. achieved maxima. Subsequently percentages of birch declined. Pollen spectra disclose that migration of spruce from the interior into this area took place within recent centuries. A climate cooler and drier than at present is interpreted from the diagrams to have been in effect during the earliest cultural phase and probably lasted until about 2500 B.P. Later, climate became slowly warmer and increasingly more humid. Temperature, however, was at first lower than at present and, coupled with greater precipitation, presumably caused heavy snow accumulation in the Aleutian Range which resulted in glacial advances during recent centuries.