Interesting slot
I was prompted by a recent addition of my own and some searching out color ensembles has led me to understand the U.S. cavalry a bit more organized than simple militia without uniforms. Certainly during the revolution there were uniformed troopers by the height of the conflict. While I can't be certain this plank carving represents the green and red of the 4th light dragoons organized at the behest of Washington, the only other color combination that seems to fit would be Austrian. This came out of California, so who knows where it's life began. Here are a couple of quick snaps. So, maybe.
http://fourthdragoons.com/History.html
My Virginia heritage also relates to early militia cavalry stuff
Cheers
GC