More recent lava flows left rhyolite as the dominant rock in that area. Limestone, however, is a sedimentary rock common in areas outside the caldera, including the students' location in Mammoth Hot Springs. But the park ranger had more up her sleeve. When the students gathered in a circle to discuss the mysteries, Doss said the white rock is actually called travertine, a particular form of limestone that was deposited on the surface by a hot spring that once flowed there. A white trail snaked across the ground near the students, showing where hot water once flowed off a nearby ledge.
Springs often become clogged and then dry up as the water begins flowing elsewhere.
Trees stood lifeless and bare at the edge of the Travertine trail. The park ranger asked her students about the mystery of the dead trees. Some wondered if the 1988 fires burned them. Others, thinking about experiments that showed acidic spring water in the Norris Geyser Basin, said the culprit might be similar water. These trees were buried alive.