We want to see if there's any surface indication of what's buried in the ground. They represent a certain time and a certain environment. Some rocks are more promising than others for fossils. Roeder's workers painstakingly examined more than 50 Eastern Toll Road sites where major fossils were found, collecting soil and screen-washing it to sift out teeth, bone fragments and other tiny fossils. Screen-washing 20 buckets of clay soil might result in one bucket of sand and small fossils, Roeder said.
Fossil hunters can be surprised, however.
The Loma Ridge area has Puente Formation rocks, typically containing fish fossils. A mastadon elephant was hardly characteristic. There are probably only 15 to 20 places in California where dinosaur material has been found. What monitor Gino Calvano found in Blind Canyon, north of Santiago Canyon Road, were neck bones and a toe bone of what appears to be a duckbilled dinosaur, Roeder said. To the untrained eye, they didn't look like much - black, porous places inside gray rock.