File:Warren Map of the Territory of the United States from the Mississippi to the Pacific Ocean 1857 UTA.jpg

English: U.S. Army Topographical Engineer Lieutenant Gouverneur K. Warren's map of the trans-Mississippi west is considered one of the great cartographic accomplishments of the nineteenth century. It was a synthesis of the most important maps of the area from about 1810 to 1857. Warren (1830-1882), later a Brigadier General and hero of the Battle of Gettysburg, constructed the map over a period of four years and wrote an approximately 100-page "Memoir" to accompany it. He consulted the maps of virtually every U.S. government-sponsored expedition in the west, from Lewis and Clark in 1804-1806 to the more recent exploring expeditions for the U.S. Pacific Railroad Surveys and the U.S.-Mexico Boundary Surveys. Warren also included their survey routes on his map and noted existing U.S. Army forts or posts. The combined map helped the government authorities then determine areas needing further exploration. For example, a vast stretch of the southern Utah Territory is labeled "Unexplored". By the time the map was published in 1857 new expeditions were already on their way there.

This example is divided by military districts, uses red flags or guidons to emphasize the U.S. Army's forts or posts, and is hand-colored in delicateshades of yellow, pink, and blue to show vast stretches of territory still largely dominated by specific Native American tribes. Military planners could have used this example to plot their next campaigns or to determine possible locations for new forts.

It is important to note that despite its large size, Warren's map does not show as much detail as the almost equally large U.S. Army Topographical Engineers' Map of Texas (cat. no. 61), which had less area to portray.