A year later, in July, 1879, Walcott was appointed to the newly formed U.S. Geological Survey. Over the next several field seasons, he and his comrades charted the geology of sizable segments of Arizona, Utah, and Nevada, including unexplored parts of the Grand Canyon, where in 1883 he first reported discovery of Precambrian specimens of Cryptozoon (Walcott, 1883). Other finds soon followed, with the most startling in 1899—small, millimeter-sized black coaly discs that Walcott named Chuaria and interpreted to be “the remains of . . . compressed conical shell[s],” possibly of primitive brachiopods (Walcott, 1899). Although Chuaria is now known to be a large single-celled alga, rather than a shelly invertebrate, Walcott's specimens were indeed authentic fossils, the first true cellularly preserved Precambrian organisms ever recorded.