I found this on the Bureau of Reclamation Website http://www.usbr.gov/cultural/fossil.html
The public has an opportunity to view fossilized plants and marine animals and even fragments of dinosaur bones in their natural setting at the Cottonwood Creek Dinosaur Trail, located about 25 miles southwest of Casper, Wyoming, at Reclamation’s Alcova Reservoir.
The rock formations along the trail include many invertebrate, vertebrate, and plant fossils, indicating a rapidly changing environment of deposition 200-140 million years ago with tidal flats, sand dunes, beaches, oceans, storm deposits, and complex stream and river systems.The best remaining examples of dinosaur bones can be seen near the top of Cottonwood Creek Dinosaur Trail, which is approximately 2 miles long and rises nearly 300 feet in elevation.
The extreme, unstable slopes and switchbacks contribute to continually changing trail conditions. The trail user should be in good physical condition and exercise caution. Due to the rugged terrain, the trail is not accessible to the mobility impaired, although interpretive signs located at the trailhead are accessible. Estimated time to complete the self-guided tour along the trail is 2-3 hours. Collection of fossils by the public is prohibited along the trail. For additional information, contact Jay Dallman or call (307)261-5608.