from Fort Leavenworth, in Missouri, to San Diego,in California, including part of Arkansas, Del Norte, and Gila Rivers (1848)

After the start of the Mexican-American War in 1846, a military expedition was sent out from Missouri to the northern portions of Mexico (what is now New Mexico, Arizona, and southern California) to capture the town of Santa Fe and continue westward to secure territory in California. The "Army of the West" included Lt. William H. Emory, a topographical officer who also served as the expedition’s naturalist, recording the plants he encountered and describing the terrain and the native peoples and cultural artifacts.

Accompanying the expedition was John Mix Stanley, an artist who later became renowned for his portraits of Native Americans. During this reconnaissance, he produced 26 illustrations of Native Americans, landscapes, and natural history, including the first images of the giant saguaro.

The expedition's route crossed a portion of the Sonoran Desert that was botanically unexplored at this point. The 14 botanical plates in the report are the first scientific illustrations of such unique Sonoran Desert plants as the ocotillo, creosote, Apache plume, and Mexican marigold.

In addition to the military success of the expedition, it also produced the first American account of the peoples, geography, and botany of the region and the most reliable map to date of the territory soon to become part of the United States. Emory compiled the expedition’s findings and maps in Notes of a Military Reconnoissance that was published by the Thirtieth U.S. Congress in 1848. The report was published repeatedly and became a popular travel guide for settlers traveling to California.