Located in the floodplain of the Missouri River near present-day Omaha, Nebraska, it was the temporary winter camp of the scientific party of the Yellowstone Expedition.

From October 1819 to June 1820, the party studied the geology and biology of the vicinity, and met with the local indigenous peoples.

President Thomas Jefferson was eager to see these resources exploited, believing that fur trappers and traders with the local indigenous peoples would serve as the vanguard of American expansion into the new territory.

[4][5][6] In 1818, to counteract this British influence, and to protect American territory and fur-trapping activity in the upper Missouri watershed, President James Monroe and Secretary of War John C. Calhoun proposed, and Congress authorized, the Yellowstone Expedition.

Over 1000 soldiers, led by Colonel Henry Atkinson, were ordered to travel up the Missouri and establish a chain of forts in its upper reaches.

In early 1817, he had suggested to President-elect Monroe that an expedition be mounted to explore and map the Great Lakes and the upper Mississippi watershed by steamboat.

The party included William Baldwin, doctor and botanist; Augustus Edward Jessup, geologist; Thomas Say, zoologist; Titian Peale, assistant naturalist; and Samuel Seymour, artist.

To impress the indigenous peoples who beheld it, it bore "an elegant flag representing a white man and an Indian shaking hands, the calumet of peace and the sword",[13] and the bow was formed in the shape of "a huge serpent, black and scaly ... his mouth open, vomiting smoke".

Of the five steamboats hired to carry the force upstream, two apparently never reached the Missouri; another gave out and had to be left behind 30 miles (50 km) below Franklin; and the remaining two had to be abandoned a short distance above the mouth of the Kansas River.

[21][22] On September 17, 1819, the Long party reached Fort Lisa, a fur-trading post located a few miles north of present-day Omaha, Nebraska.

Intended to be a permanent post, Cantonment Missouri was destroyed by floods the following spring, and abandoned in favor of a new site, Fort Atkinson, atop the bluffs and out of the floodplain.

[33] The scientific party's eight-month stay at Engineer Cantonment produced what has been called "the first biodiversity inventory undertaken in the United States".

By contrast, the long stay at Engineer Cantonment allowed the party to study the local biota in detail, and to try to produce a complete inventory of the plants and animals of the area.

The loss of Baldwin en route to Engineer Cantonment had left them without a botanist; James, his replacement, did not arrive until a short time before the departure of the summer 1820 expedition.

At the time of the Long expedition, the Missouri was a meandering stream subject to spring flooding, moving through a wide floodplain with oxbow lakes and palustrine wetlands.

This phenomenon has been observed with other birds, mammals, and insects of the eastern woodlands: their ranges have expanded with the spread of riparian forest upstream along prairie rivers.

During the 20th century, there were some desultory attempts to find it; the failure of these led to the general belief that the remains of the site had been obliterated by flooding and cutting of the river, by quarrying operations, or by other modern development.

A trench was dug at the putative site, which produced limestone fragments, some discolored by burning, possibly remnants of a fireplace.

Screening of dirt taken from the trench in the area of the burned limestone yielded, among other things, a brass button and a trigger guard fragment similar to items found at Fort Atkinson.

Fragments of ceramic tobacco pipes and tableware of a sort used around 1820 tended to support the conjecture that the site was actually Engineer Cantonment.

[47] The quality of the items also lent support to the conjecture: while tin cups and utensils would have been used by common soldiers, the wine bottles and painted porcelain found at the site were consistent with the upper stratum of society to which the expedition's scientists belonged.

Although the oxbow was no longer extant in the early 21st century, trenching east of the two-room building discovered the edge of the harbor.