| A Death Valley visitor stands on the Rest Spring Gulch fossil horizon in the Upper Mississippian Perdido Formation. The fossil-rich zone occurs at the very top of the Perdido, in a narrow five foot-thick bed consisting of grayish red to grayish purple, extremely soft shale, which is in turn capped (overlain) by a six inch to one foot-thick layer of dark-gray, fine-grained limestone bearing abundant Cravenoceras ammonites,horn corals, brachiopods, orthocone nautiloid cephalopds and crinoid columnals. The Perdido Formation includes most of the rocks in the immediate foreground (roughly lower third of image). In the middle ground lies the Upper Mississippian Rest Spring Shale, which consists of several hundred feet of drab olive-gray siltstones and shales; the unit is sparsely fossiliferous, yielding for the most part rare fragmentary remains of terrestrial plants. In the distance, along the skyline, can be seen a prominent rounded mountain top composed of the Lower Pennsylvanian Tivipah Limestone; fusulinids and brachiopods have been reported from the carbonate sequence. |