A three-foot-thick sandstone bed visible on both sides of the trail contains a layer of rock with fossil Turritella aedificata snails, called “Tower Shells” for their slender tapered shape and characterized by seven or eight coils or “whorls.” During their lives, these snails crawled along the ocean bottom and ate algae, and Turritella are ancestors of some modern snails. The rock layers were originally formed in a horizontal position, but as Mount Diablo uplifted, the beds were tilted 90 degrees, leaving the upturned eroded edges visible today. Geologists estimate these sedimentary rocks are approximately 45 million years old. Fossils in sedimentary rocks provide valuable information about Earth’s history by revealing the animals and plants that lived through geologic time, helping explain past climates, offering clues to past events, and helping date the age of rocks and the environment in which the rocks were formed. Turritella has helped geologists better understand the geologic history of Mount Diablo.