The spear point you illustrate looks very much like some of the
notched points from the Texas archaic, rather than the high plains of
Wyoming.  We do find them here once in awhile, however.  I have seen one or
two from a site in the Bighorn Basin on Medicine Lodge Creek.  I estimate
that it is around 3,000-4,000 years old or so.  The material yours is made
out of looks like the chert that outcrops in the Bridger Formation around
Flaming Gorge in southwestern Wyoming.