During late July and early August of 1804, the Lewis and Clark Expedition traveled the length of the Missouri River that today forms the border between Iowa and Nebraska. Meriwether Lewis and William Clark studied the river, forests, and prairies, often hiking along the riverbanks and exploring inland while other crew members kept the keelboat and pirogues moving upriver. In his journal, Clark described the river bluffs and tall grass prairie, comparing the bluffs to the head of a bald man and writing that the prairie stretched "as far as my sight will extend." While hunting elk, he once found the endless prairie so entertaining that he forgot the promise of fresh game for dinner and spent several hours studying the plants and soil instead. Clark also wrote about the yellow clay of the Loess Hills, and although he did not call them by that name, he may have been the first American to write about this steep ridge of hills beginning in northwestern Missouri and continuing for 200 miles along the western edge of Iowa. President Thomas Jefferson had predicted in his instructions to Lewis and Clark that the plants, animals, and land would be worthy of notice, and in this region members of the expedition found that this was so.