165 million years ago, Thermopolis, Wyoming was covered in a shallow ocean called the Sundance Sea. This was a shallow, inland sea that extended across parts of the North American Continent during the Middle to Late Jurassic Period. Evidence suggests that this deposit was created by a series of events that caused the ocean to progress and regress repeatedly across the continent.
Above the Sundance Formation lies the Morrison Formation, deposited roughly 150 million years ago. This distinctive sequence of sedimentary rocks has been among the most fertile sources of dinosaur fossils in the entire world. It is within this formation that the Wyoming Dinosaur Center staff focuses their search for fossils. Finding new places to dig is the first step in the paleontological process and it takes both keen observational skills and patience. One thing out there to help us is erosion which exposes new material every year. Over the past 24 years, WDC field technicians have found and identified over 130 dig sites on the Warm Spring Ranch.