THE CLARKIA FLORA: ITS DIVERSITY AND STRATIGRAPHIC POSITION RELATIVE TO OTHER MIOCENE FLORAS OF THE COLUMBIA PLATEAU

The Clarkia flora, located in the upper St. Maries River Valley of northern Idaho, is an exceptionally well-preserved and very diverse paleontological assemblage. Preservation includes detailed impressions and compressions of both foliage and reproductive organs. 48 families represent the flora. These families include 98 genera and nearly 150 species. The flora includes nearly all the species found in the many sites described in Chaney and Axelrod's, Miocene Floras of the Columbia Plateau (1959). Of particular interest is the large diversity of conifer remains. There are 15 confirmed conifer species with several more possible. Animals are represented by many species of insects, two species of bivalves and one gastropod. There are also three species of fish. Recently found were the teeth of three rodents (two species). In the last twenty years detailed work by many geologist working for the Department of Energy (GSA Special Paper 239, Reidel and Hooper, 1989) on the high level nuclear waste repository has resulted high degree of stratigraphic resolution of the Columbia River Basalt Group. This resolution enables us to more precisely position the many floras preserved in the sediments of the lakes that were created by the basalt flows. Most of the known sites fall within three groups. The first is within the Imnaha Formation (17.5 to 17m.y.). The second is just below or associated with the R1 Member of the Grande Ronde Formation (16.5 m.y.). The third is just below or associated with the Priest Rapids Member (14.5 to 15 m.y.) of the Wanapum Formation. The latter was the damming flow for Lake Clarkia.