About 55 million years ago during the Late Paleocene epoch, Wyoming was a warm, subtropical swamp where giant cypress trees like those now found in Louisiana's Pointe Lake grew. Some of these ancient trees were buried under sediment and turned to stone, and the three petrified trees here were found during coal mining operations at the Eagle Butte Mine near Gillette. In warm wetlands, dead vegetation accumulates as peat below the water line, where bacteria turn it into a dark gel; as this material is buried under new layers of plant matter and peat, heat within the earth drives off moisture over millions of years and converts the residue into coal. Other tree trunks, submerged in muddy, low-oxygen swamp conditions, are protected from decay as silica dissolved in groundwater soaks into the wood and, through petrification, replaces the plant tissues with minerals to form a crystalline cast of the tree. The orange and red colors in these examples indicate iron oxide along with silica. The petrified tree next to the front door of the Visitor Information Center has visible rings that suggest it was about 300-500 years old when it died millions of years ago, while the larger tree nearby probably lived much longer, and mature cypress trees in this area reached between 1,200 and 1,500 years of age.