As part of its 2001 archaeological field season, the Wyoming State Archaeologist's Office and the Department of Anthropology, University of Wyoming, conducted an archeological study (including geophysical remote sensing survey and excavations, view map) on the 1852-1855 Oregon Trail trading post called “Seminoe’s Fort” or “Semino’s Trading Post” located near Devil’s Gate, Wyoming. Specifically, they examined the remains of the main structure of the trading post, and eight associated, ancillary structures that formed the compound. The site is part of the Devil’s Gate historic region, with several interpretative paths and signs established by the BLM and the Mormon Church. Identification and interpretation of the exact location of the trading post was critical to the development and interpretation of the local historic site area (Martin Handcart Interpretive Center). Even more critical was identification and study of architecture data of the structure. While much is known about the historic record of the Mormon Pioneer and Oregon Trails, there is also little known about specific locations such as this on the trails. Many historic documents are contradictory and archeological investigations clarify many of these.

An interpretive sign at Devil's Gate Historic Site and published material say the post was run by Basil Lajeunesse. Unfortunately, Basil was killed by Modocs in Fremont's camp at Klamath Lake in 1846, long before the post at Devil's Gate was built. Seminoe's Fort was built and run by Basil's older brother, Charles Lajeunesse, from 1852 to 1855. His French Catholic baptismal name was Simono, or Little Simon. Charles built the trading post in 1852, using timbers from the Ferris Mountains, about 20 miles south of the post’s location. Lajeunesse occupied the post for three years, returning to St. Louis every winter to restock goods. The location chosen by Charles for this trading post was ideal. First it was almost half way between Fort Laramie to the east and Fort Bridger to the west, other restocking locations along the overland emigrant trails. Second, the area chosen was one of the few locations along the Oregon, California, and Mormon Trails, where all three trails came together and followed a single set of ruts. Usually these trails were spread out over a wide distance. Finally, based on the archaeological evidence, the front door of his trading post was within 20-30 feet of where the trails passed. All emigrants along the trails between 1852-1855 had to pass the trading post. They just couldn’t miss it. Lajeunesse abandoned the post to the Sioux in 1855, the year before two Mormon Church Handcart Companies of emigrants came through the region and were caught in an early winter blizzard in November 1856. Apparently, the buildings stood empty through the 1856 emigrant season. They were beginning to collapse by the fall of 1856, when the Martin Handcart Company and Hunt and Hodgett Wagon Trails took refuge during the blizzard. Lajeunesse never re-occupied the trading post, although apparently various activities of the Mormon Church were conducted there the following year until it was burned in the fall of 1857.

Archaeological investigations in 2001 revealed a distinctive architectural style was used throughout the construction of the nine buildings in the trading post. This consisted of vertical posts placed a minimum of two to three feet into the ground, flat foundation rocks placed between the posts and then logs cribbed up to form the walls, with nails holding the logs to the posts. It appears at least five of the nine recorded foundations were constructed in this manner. Foundations of the remaining four cabins were not as obvious in the archaeological record. During the early 1860s (probably 1863, according to some emigrant diaries), another cabin was built within the limits of one of Seminoe’s cabins, using foundation rocks from these four earlier cabins, an adaptive reuse of construction materials. Artifacts recovered from the excavations and positions of the 1850s structures relative to the Oregon Trail have helped identify the trading post building, a blacksmith shop, store rooms and living quarters.

During the summer of 2002, a reconstruction of the trading post will be built near the original location, as part of the Mormon Church interpretation of the Martin’s Handcart Company Disaster of 1856.