The label on types of this subspecies, in the Academy of Natural Sciences of Philadelphia, states merely "near Bridger's Pass, Wyo., Expedition of 1856, Dr. W. A. Hammond" (letter from Dr. James Böhlke to Cross, dated Jan. 27, 1960). Dr. Hammond was a surgeon who also collected scientific specimens, assigned to an expedition under the command of Lt. F. T. Bryant. Bryant's log is recorded in the Proceedings of the 35th Congress (1858:455-481). The site at which these specimens were taken cannot be ascertained from the log, but study of it is helpful in indicating the probable locations.
The expedition left Fort Riley on June 21, 1856, on the following route: up Republican River; across to Fort Kearney on Platte River; west along Platte River to S. Platte River; up S. Platte River to Pole (Lodgepole) Creek; Pine-Bluffs (Neb.-Wyo. line); across East Fork to West Fork of Laramie River; Cooper's Creek; West Fork of Medicine Bow; Pass Creek and down canyon of Pass Creek; across N. Platte River; up Sage Creek; on August 15, camped on Muddy Creek, tributary to Green River (first record of fish, trout); back to Sage Creek; August 19-21, camped on island in North Platte River; to Pass Creek; Elk Creek; west branch of Medicine Bow; Aspen Creek; West Fork of Laramie River; August 29, to East Laramie River where a large supply of fish was caught; tributary of Cache la Poudre then downstream to mouth of this river; down South Platte River past mouth of Crow Creek and Beaver Creek; left South Platte River 14 miles below mouth of Beaver Creek, toward Republican River; down Rock Creek to Arikaree; down Arikaree to Republican River and down the Republican to Fort Riley.
Mention is made of fish only twice in the entire log. We doubt that Muddy Creek or the East Laramie River is the type locality of _P. gulonellus_, because the flathead chub has not since been found in either of these streams. The most likely collection site for _P. gulonellus_ is the North Platte River near the mouth of Sage Creek, in what is now Carbon County, Wyoming, where the expedition was camped for three days. This species is known to occur in the North Platte River, and since the type locality is reported as "near Bridger's Pass" this is the probable location.