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Oxygen isotope ratios of pedogenic carbonates were analyzed along a climatic gradient in the Palouse region of eastern Washington State to evaluate changes in their isotopic composition with changing climate. A modern analog approach was used to assess the relationship between the istotope ratios in the pedogenic carbonates with those in soil water (measured in June when we anticipated carbonate formation might occur because of low soil water content), and meteoric water from two National Atmospheric Deposition Program (NADP) sites adjacent to our sequence. Mean annual meteoric water delta(18)O values (wrt VSMOW) from the two NADP sites varied slightly with elevation, -13.9 parts per thousand at the Starkey site (elevation 1253 m) and -13.0 parts per thousand at the Palouse site, (elevation 766 m) but showed distinct seasonal trends with weighted means ranging from -11.9 parts per thousand during autumn to -15.0 parts per thousand during the winter. Carbonate delta(18)O (wrt VPDB) varied significantly with MAP, ranging from -14.1 parts per thousand at the most arid site to -11.4 parts per thousand at the wettest site but displayed a trend opposite to that of soil water delta(18)O (-4 to -12 parts per thousand VSMOW for the 70 cm depth). Neither measured soil water delta(18)O values nor mean meteoric water delta(18)O values generated realistic temperatures of formation for the observed trend in carbonate delta(18)O values. When mean annual temperatures across the gradient were used for temperature of formation, calculated soil water delta(18)O in equilibrium with carbonate delta(18)O was similar to winter precipitation delta(18)O at the most arid sites but became increasingly similar to mean annual meteoric delta(18)O as MAP increased. We suggest that the unexpected trend in carbonate delta(18)O is largely due to the diminishing influence of winter precipitation/snowmelt on soil moisture as MAP increases across the climatic gradient and that seasonal effects of meteoric water may need to be considered in pedogenic mineral isotopic equilibrium in temperate regions.