This colorful geological map was done by Professor N.H. Winchell and published in "Report of a Reconnaissance of the Black Hills of Dakota, made in the summer of 1874 by William Ludlow. The map is attractively colored to bring out the geological findings. It is interesting to note that the troops accompanying the surveyors were under the command of L. Col. G.A. Custer and were not molested by hostile Indians. Just two years later the major engagements of Crook at Rosebud and Custer at Little Big Horn would take place in the same general area.