This finely engraved map covers the northern two-thirds of the United States from the Great Lakes to the Pacific Ocean. The various routes of Lewis and Clark are detailed in red overprinting with line styles to differential travel over land vs. by water. A finely lithographed map printed in color by Julius Bien. This is one of three large folding maps included in Volume IV of what is considered one of the best works on the expedition. Published in a limited edition of only 1,000 sets, this map is a scarce issue and a beautiful example.