Bob, regarding Col. David Shanks, I just discovered that he was buried in Laramie, Wyoming. There's a newspaper article from an 1884 Laramie newspaper stating that among the graves decorated Memorial Day was that of "Colonel Shanks" "Confederate".
The cemetery is I believe the Old Fort Laramie Post Cemetery, now defunct.
He was alive there in 1870. My guess is that he died there around late-1870 to early 1871.