Capt. Lewis did describe one fox that has been determined not to be a red fox variant.
Capt. Lewis, July 6, 1805--There is a remarkable small fox which associates in large communities and burrow in the praries something like the small wolf but we have not as yet been able to obtain one of them; they are extreemly watchfull and take reffuge in their burrows which are very deep; we have seen them no where except near these falls.
Capt. Lewis, July 8, 1805--The party who were down with Capt Clark also killed a small fox whichthey brought with them. it was a female appeared to give suck, otherwise it is so much like the comm[on] small fox of this country commonly called the kit fox that I should have taken it for a young one of that species; however on closer examination it did apear to differ somewhat; it’s colour was of a lighter brown, it’s years proportionably larger, and the tale not so large or the hair not so long which formed it. they are very delicately formed, exceedingly fleet, and not as large as the common domestic cat. their tallons appear longer than any species of fox I ever saw and seem therefore prepared more amply by nature for the purpose of burrowing. there is sufficient difference for discrimination between it and the kit fox, and to satisfy me perfectly that it is a distinct species.
Capt. Lewis, July 26, 1806--we saw a few Antelopes some wolves and 2 of the smallest speceis of fox of a redish brown colour with the extremity of the tail black. it is about the size of the common domestic cat and burrows in the plains.