Asking for a friend who is curious about the history behind Signal Butte's name and it's use by the calvary to transmit messages/information with a mirror, to a recipient located as far away as the black hills of S.D!? Any truth to this? If so, where could more detailed info be found?

I know I wrote a history column on Gen.Miles and the heliograph but I can't find it right now. Just got off work and mind is mush. But, yes, it's a true story. Google Heliograph. Nelson A. loved that gizmo.