A survey of approximately 60 ponds in the Gunnison Basin, Gunnison and Pitkin counties, Colorado, USA, showed a correlation between the thermal ranges of the ponds and the life history pattern of A. tigrinum populations. Characterization of physical and biotic parameters allowed a ranking of ponds from warm to cool, verified by temperature data taken through 2 warm seasons (1974 and 1975). The life history pattern of the salamander populations was determined on the basis of the number of size classes of salamanders observed in the pond. A model is proposed relating the thermal regimes of the pond and the observed life history pattern of the salamanders. Three life history patterns are defined for these populations: standard life history, only 1 size class of larvae; neotenic life history, 2 size classes of larvae with metamorphosis occurring in the 2nd warm season; and neotenic and pedogenetic life histories, 3 or 4 size classes of larvae with metamorphosis occurring in the 3rd or later warm season.