The Lewis and Clark Expedition, officially the Corps of Discovery, traveled through what is now South Dakota from August 21 to October 14, 1804, and from August 21 to September 4, 1806, making numerous observations of animals, plants, birds, and fish previously unknown to science, including the pronghorn antelope, which they called goats, the prairie dog, which they called barking squirrels, the mule deer, coyote, great gray wolf, prairie rattlesnake, northern jack rabbit, a different kind of porcupine, and the black billed magpie, then thought to exist only in Europe. They also met a number of Indian tribes, distributing gifts and giving speeches about the great white father in Washington, and although there were a few tense moments, they fought no battles with the tribes they encountered in present-day South Dakota. In the Springfield area, they passed through on September 1-3, 1804, moving among very high bluffs of yellowish-red, brownish, and white clay as hard as chalk, landing on the lower end of Bon Homme Island and camping there on the night of September 1. On September 1, 1806, they stopped on the same island to hunt and took only one elk, prompting Clark to remark that this brought two years together. Near the island they saw what they believed were the remains of an ancient fortification, and Clark spent several hours measuring and drawing it, though this feature, one of the two most elaborate on the Missouri, was later determined to have been formed by river flooding that deposited sand over many years. On September 3, Clark noted great quantities of delicious plums near Plum Creek, an area historians believe is present-day Emanuel Creek just west of here.