Fremont's map, showing his explorations between 1842 and 1844, is one of the most important maps of the Western United States issued in the first half of the 19th Century.
Wheat noted that " John Fremont's map of 1845 represented as important a step forward from the earlier western maps of the period as did those of Pike, Long, and Lewis and Clark in their day."
By the 1830 America's knowledge of the west was still confined to the region of the upper Missouri. Then along came the explorer and trapper Jedidiah Smith. Before he was killed by the Comanche Indians in May 1831, Smith had discovered the southwestern trail to California and explored the Great Basin, the Sierra Nevada and the Pacific Coast in search of furs. During his last winter, Smith prepared a map with the help of a young surveyor Samuel Parkman. This great map has been lost but the data was transferred 15 years later on to this Fremont map.
John Charles Fremont (1813-90) was a young and ambitious lieutenant in the Corps of Topographical Engineers who cut his teeth working with the Frenchman Joseph N. Nicollet during the first truly scientific survey of the interior during 1838-39. He was the son-in-law to the powerful Senator Thomas Hart Benson from Missouri and under his influence he undertook three main expeditions to the west.
The map is from the 'Report of the Exploring Expedition to the Rocky Mountains ...' It takes in the entire West from Westport and Kansas to the west coast. The interior includes the first accurate depiction of the Great Salt Lake, some of which was noted during Fremont's cruise on the lake in a rubber inflatable boat. The top of the map bears a profile of the route from the mouth of the Kansas River to the Pacific Ocean. 'Though the Oregon Trail and the Spanish Trail had been regularly used for a few years there were no dependable maps. For other parts of Fremont's route, much of the recording of his map was new, including the whole extent of the zsierra Nevada Range, the California rivers from the American River south, and the three Colorado rivers' (Streeter). It is hard to overestimate the influence of this map.
Wheat states that the map " radically and permanently altered western cartography." The accompanying report states only facts and accurately mapped locations were included. The map left only minor areas unmapped or unexplored with the exception of the Great Basin. Wheat went on to state that " To Fremont and his magnificent map of his Second Expedition all praise. This is an altogether memorable document in the cartographic history of the West, and for it alone Fremont would deserve to be remembered in history."
The map was to have a powerful effect on the routes taken in the California Gold Rush.The map is the House Issue and is drawn with the assistance of Charles Preuss who was born in Waldeck, Germany, in 1803. Arriving in the United States in 1834 Fremont hired him as a cartographer and draughtsman. Preuss would go on to draw both of Fremont's other highly important maps of the west.