During the last Ice Age, the Bay Area was a vast river valley roamed by mammoths, saber-toothed cats and giant sloths. Many of them are still down there in the ground, in fossil form, only to be discovered when construction crews start digging for big projects like skyscrapers and transit tunnel. These animal artifacts have scientific value and, as Indiana Jones would say, belong in a museum. That’s where people like Jim Walker come in. Walker is a senior paleontologist/geologist for Applied Technology and Science, a San Francisco engineering and environmental-consulting firm. His job is to monitor construction sites for fossils and, when they’re discovered, get them out of the dirt quickly and into safe storage. Walker has worked on some of the largest government and private projects in the Bay Area, including the $2.2 billion Transbay Transit Center in San Francisco, the $810 million Calaveras dam seismic retrofit and the $300 million Samsung corporate headquarters in San Jose.