Palynological analyses of microfossil assemblages from Upper Cretaceous and lower Tertiary rocks in British Columbia and adjacent Alberta indicate major differences in the evolution of floras between coastal and interior locales. The Santonian-Campanian assemblage on the coast is dominated by an assemblage of ferns, herbaceous angiosperms, and Proteacidites, whereas the assemblage from beds of similar age in western Alberta is typified by different species of ferns, probable herbaceous angiosperms, and Aquilapollenites. These differences suggest the existence of two floral provinces during Santonian-Campanian time, possibly separated by the western cordillera. A late Maestrichtian-Danian assemblage from the Rocky Mountain trench contains a taxodiaceous-angiosperm complex that differs from an assemblage of essentially the same age in the western interior region (eastern Montana-western South Dakota) of the United States, suggesting again the presence of two different floral provinces at this time. A comparison of middle Eocene assemblages on the coast with those of the interior plateau regions of southern and central British Columbia shows a coastal assemblage composed of ferns and mainly herbaceous angiosperms, whereas the comparable assemblage east of the Coast and Cascade Mountains contains a predominantly coniferous-hardwood flora.