Fig. 10. Structural relation of older rocks to Wasatch and Green River formations near Prow Point in the northwest corner of the monument (from U.S. Department of Interior 1964).
PALEONTOLOGY
Fossils of plants, invertebrates, and vertebrates are abundant in rocks exposed in the Fossil Basin. For example, Oyster Ridge received its name because of the well-preserved and abundant fossil oysters found there. Of course, Fossil Butte and Fossil Butte National Monument were so named because of the beautifully preserved fossil fish. A brief review of the main groups of fossils to be found in the basin follows.
Flora
Many of the sediments in the Fossil Basin contain an abundance of fossil plants. These consist of pollen, spores, wood, and leaf impressions. Those of the Green River Formation are best preserved and have received the most study.
Brown (1929, 1934) and Lesquereux (1883) have presented the best information on the flora of the Green River Formation. Much of the present knowledge is based on their work.
Brown (1929, 1934) concluded that the Green River flora is a mixed forest type. It contains some plants common to warm, wet lowlands and others adapted to cooler, drier uplands. Pollen studies support Brown’s original concept that several plant communities, including mountain communities, existed around Fossil Lake.
The flora was situated in an inland, mountain basin. Fossil Lake was in the middle of the basin. Swamps and flood plains bordered the lake, while the flanking ridges and mountains provided altitudinal variations in the plant assemblage.
Spruce, fir, and pine are indicated by fossil pollen. The presence of these conifers suggest that at least some of the nearby mountains rose to heights of 6000-8000 ft.