Abstract This field trip covers sedimentological and paleontological research being conducted on the Jurassic Aztec Sandstone and Lower Cretaceous Willow Tank Formation in Valley of Fire State Park. Valley of Fire State Park is located in southern Nevada, just outside of the town of Overton. The Jurassic Aztec Sandstone is equivalent to the Navajo and Nugget Sandstones; these formations together record an aerially large erg complex along the western margin of North America during the time of deposition. Invertebrate and vertebrate ichnofossils are not uncommon in portions of these Jurassic formations. The Willow Tank Formation is composed of the deposits of both a braided and anastomosed fluvial system. This system drained off the paleohigh of the Sevier fold and thrust front to the west, during Early Cretaceous time. Recently a diverse vertebrate assemblage has been discovered from this formation. The fauna of the Willow Tank Formation are similar to other Early Cretaceous faunas from western North America. The vertebrate remains recovered include three taxa of fish, three to four taxa of turtle, crocodilian, iguanodontian, thyreophoran, dromaeosaur, tyrannosauroid, two theropod ootaxa, and a titanosauriform. In addition to the vertebrate elements, two fern morphotypes have been found. Through the course of this field trip participants will see extensive exposures of Aztec Sandstone, including vertebrate ichnofossils. Participants will also hike to vertebrate bearing-beds of the Willow Tank Formation.

Abstract Eocene nonmarine sedimentary rocks that occur in northwest and central Washington as a widespread series of outcrops are evidence of a meandering river system that existed prior to the mid-Tertiary uplift of the North Cascade Range. Arkosic strata appear to have initially been deposited in a basin that was later divided by strike-slip faulting, producing outcrops of the Swauk Formation on the eastern flank of the North Cascades, and the Chuckanut Formation to the west. Plant fossils are abundant in both formations, but the Swauk paleoflora has received little study. The Chuckanut Formation paleoflora records a marked shift in the region’s paleoclimate. The Late Paleocene to Middle Eocene Bellingham Bay and Slide Stratigraphic Members, which comprise the lower 6000 m of the formation, contain diverse assemblages of subtropical plant fossils. In contrast, the overlying 3000-m-thick Padden Member contains taxa indicative of a warm temperate paleoclimate. An unconformity may separate the Padden Member from older Chuckanut strata, and the age of the Padden Member has not been determined. The climate shift may have been a Late Eocene fluctuation, but the possibility that the floral changes represent the transitional Eocene-Oligocene cooling event cannot be discounted. Animal fossils from the Chuckanut Formation include aquatic mollusks and a soft-shelled turtle, and track impressions from a variety of birds and mammals.