MAP 8.1 Lewis and Clark and Zebulon Pike Expeditions, 1804–1807 The expeditions led by Meriwether Lewis, William Clark, and Zebulon Pike illustrate the vast regions explored in just four years after the U.S. purchase of the Louisiana Territory. Journeying through and beyond the borders of that territory, the explorers gathered information about Indian nations, plants, animals, and the natural terrain even as Comanche and Shoshone nations, with access to horses, transformed the region.