I have sourced the origins of the map from the oracle (Elisabeth) on the south coast of England. To summarise;
Seems to be a Godfrey/Cyrus T. Brady effort. There is a version in pencil printed in Mike Donahue's Drawing Battle Lines, however, the version in the book is a rougher version than the one posted here, possible done in pencil. Someone -- presumably Brady, since the lettering's in exactly the same style -- must have re-drawn it nicely in ink for the version posted above. The pencil one is undated, and is captioned: "Plan of Reno's defense on the bluff. Original sketch Col. E. S. Godfrey U.S.A. Drawn by Cyrus T. Brady". Actually, "Col." ought to help a bit with dating it -- as Godfrey became a Colonel in 1901, and was promoted to General in 1907. Brady's book, Indian Fights and Fighters, was published in 1904; possibly he did the more refined version for that?