Wood X-ray densitometry (inter- and intra-ring wood density, ring width) and measurements of tracheid length were used to evaluate wood structural variability in 93 trees from 33 populations of white fir (Abiesconcolor(Gord. et Glend.) Lindl.). Individuals from populations representing the geographic range of the species had been growing for 24 years in a plantation near Placerville, California. Growth ring widths showed a clinal increase from northern Oregon to southern Californian populations, due mostly to variations in width of the earlywood. Rates of change from pith to bark in tracheid lengths and earlywood density decreased from northern Oregon to southern California, with the highest rates of change being among Utah populations. Slower rates of change in tracheid length and wood density would contribute to more uniform wood structure in these southern populations. Multivariate analyses confirmed the separation of regional groups within white fir. Results indicated that there is a differentiation between northern and southern Californian white fir, consistent with the former being ascribed toA.concolorvar.lowianaand the latter toA.concolorvar.concolor. Arizonan populations were grouped with southern Californian white fir.