actually what you are calling the base is the actual cortex of the piece and would be the non working end of the blade which was probably hafted sideways onto a slotted buffalo rib handle
it appears to have been the striking platform of the blank used to make it
i first thought it was broke off on that end but can see it isn't
Nice backed-knife. Is one edge of it dulled? A lot of them are (for mounting in rib or holding in hand). They were used by all cultures throughout the U.S. but are probably found most frequently on the High Plains, made by Shoshonean groups. Many collectors refer to the hand-held knives generically as Squaw Knives, but that's misleading.