America's Aquarium in Stone Some of the world's best preserved fossils are found in the flat-topped ridges of southwestern Wyoming's cold sagebrush desert. Fossilized fishes, insects, plants, reptiles, birds, and mammals are exceptional for their abundance, variety, and detail of preservation. Most remarkable is the story they tell of ancient life in a sub-tropical landscape. Monument grounds are open sunrise to sunset. The entrance road gate is closed only during severe winter storms. The upper road accessing the picnic area, Chicken Creek Nature Trail (previously Fossil Lake Trail), and scenic drive closes November 1st until the snow melts, usually by late May.