Two decades after Long's party explored the Platte River basin and deemed it a dry wasteland, another group set out to explore the American West from the west coast. In 1841, the United States Exploring Expedition, led by Charles Wilkes, sailed through the South Pacific, down to Antarctica and up the west coast of North America. The expedition produced this map of "Upper California" along the way. Notice the headwaters of some rivers, like the Cache la Poudre, are less than accurate. Most of the western interior at this time was largely unknown. A vast area is labeled "Great Sandy Plain", the dreaded equivalent of "Here There Be Dragons" to early settlers.  

Wilkes continued exploring the Pacific and finally circumnavigated the globe back to New York in 1942.  The specimens he collected on his four year expedition became the basis for the Smithsonian's collection.  Wilkes was known as a harsh disciplinarian, and may have been the real-life basis for Herman Melville's Captain Ahab.

Map courtesy of the Honorable Greg Hobbs Collection.