In 1803, the Louisiana Purchase doubled the land mass of the United States. The next year, President Thomas Jefferson sent Meriwether Lewis and William Clark to explore the new acquisition. One of his aims was to map the new Northwest territory, a vast empty space on the map of the time. He was hoping Lewis and Clark would find a water route across the continent.
Jefferson, an avid geographer, had collected the best maps and information available and passed them along to the explorers. But Jefferson and most other geographers of the time were unaware
of the size and extent of the Rocky Mountains. They assumed that the source of the Missouri River lay in a low range of hills in the northwest of the new territory, and that the Columbia flowed the opposite direction not far away.
However, the Rockies soared much higher and had sharper, more jagged peaks than they expected. Many were snow-capped all summer, and they were over 300 miles across in places. As Lewis and Clark followed the river uphill into the Rockies, they found their path blocked by an incredible series of waterfalls--40, even 50 feet high. It took 12 days to carry everything around them.
What they needed was a topographic map, or a map that indicates the contours of the land, the height of mountains and the depth of passes and canyons. Topographic maps use various colors and shading to represent various altitudes.
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