The journals of the expeditions of Long, (1820) of Ashley (1825) and of Dodge (1835) make no mention of fur-trading posts on the South Platte, although they all make reference to evidence of trapping activities along this route of travel. "Within three years after the visit of Dodge's First Dragoons, however, four adobe 'forts' were established on the banks of this stream, forming a little chain but twelve miles long.. . Three men have left us rather definite data on the location of the South Platte forts: F. A. Wislizenus, Rufus Sage, and J. C. Fremont." (Hafen, 1925, (XII) 334., see quotations from these authors under their several headings in this paper).

The story of these posts is of especial interest in connection with the Rocky Mountain National Park, as they were the centers of the fur trading and trapping operations in this area (1836-1844). Trading in buffalo robes was here more important than that in beaver skins. Travelers of the late '30's and the early '40's, using the South Platte trail, were entertained at one or another of these forts. Wislizenus (1839) noted three forts; Sage (1842-43), four forts; and Fremont (1843), four forts on the South Platte. "From these three accounts it is clear that four adobe forts existed on the South Platte in 1840." These were Fort Lupton, Fort Vasquez, Fort Jackson, and Fort. St. Vrain. Fort Lupton was built in 1830 or 1837 by Lieutenant Lancaster P. Lupton who had accompanied Colocal (Colonel) Dodge to the mountains. Sometimes this fort was called Fort Lancaster. The ruins are on the present Ewing ranch about a mile north of the town of Fort Lupton. "The fort continued in a fair state of preservation through the early settlement period, and was frequently used as a refuge during the Indian wars of the sixties."

About 1832, so it is said, Louis Vasquez built a log trading post at the mouth of "Vasquez Fork", now called Clear Creek. However, the ruins of what is locally known as "Fort Vasquez" are situated on the Fort Vasquez Ranch about a mile and a half south of the present town of Plattville. This fort belonged to Andrew Sublette and Louis Vasquez in 1839, but they sold out in 1840, according to Beckwourth, who tells of helping to erect the buildings in 1838. (Bonner, new ed. 1892, 373.) "Sage asserts that the post was owned by Lock and Randolph in 1841 and was abandoned the following year". (Sage, 1857, 200.) Sage located this fort six miles above Fort St. Vrain.

Concerning Fort St. Vrain, also known as Fort George or Fort Lookout, Hafen says that it was established in 1837 or 1838 about one and a half miles below the mouth of St. Vrain Creek. "Ceran St. Vrain was a partner with the Bent brothers in the twenties and remained with them for nearly thirty years. Then Fort Bent on the Arkansas held undisputed sway over a vast territory for almost a decade, when competing interests entered the field. To capture more effectively the fur trade on the South Platte they built a post on that stream to compete with Lupton, Vasquez, and others." (Hafen, 1924, 340). Francis Parkman, in "The Oregon Trail", describing his visit on the South Platte in 1846, says that St. Vrain's fort was "abandoned and fast falling into ruin." In 1859 and the early '60's there was a town on the spot that had ambitions to become the metropolis of the Colorado mines. A granite monument, placed by the Centennial State Chapter, D.A.R., in 1911, marks the site.

Between Fort Vasquez and Fort Lupton were the ruins of another fort noted by Sage and Fremont in 1842 and 1843. It remained unnamed in the annals of history until 1928, when Le Roy R. Hafen published, evidence that showed it to be Fort Jackson and that it had belonged to the trading company of Sarpy and Fraeb, formed in the late '30's. During the short existence of this company, it played an important part in the fur trade activity in the region that was to become Colorado." (Hafen, 1928, 9). (Hafen found his data in the Chouteau-Moffitt Collection of fur trade papers in possession of the Missouri Historical Society). Peter A. Sarpy and Henry Fraeb had been prominent in the western trade for some years before making their venture on the South Platte River. "Pratt, Chouteau & Co., successor to the Western department of a the American Fur Company (originally founded by John Jacob Astor), financed, Sarpy and Fraeb ... in the spring of 1837." Competition between the various fur trading companies became very sharp. In October 1838 Bent, St. Vrain & Co, purchased Fort Jackson, and, being less than ten miles south of their Fort Lookout (Fort St. Vrain), they had no need of Fort Jackson and abandoned it.

"In the years that have since elapsed Fort Jackson passed from remembrance and the almost level surface of the site (near the present lone) gives today but slight indication of the hidden foundation of the one-time primitive mart. The life and conditions the old fort housed and typified have as completely disappeared from the region." (Hafen, 1928, 14).