This a remarkable edition of Warren’s map that has been amended to show geological formations provided by Dr. Ferdinand Hayden, then Professor of Geology and Mineralogy at the University of Pennsylvania. It illustrates the geology of the northwestern Great Plains region extending from the Canadian border south to Pueblo, Colorado, and from the Colorado Front Range east to Leavenworth, Kansas. The map itself provides a comprehensive view of the surveys and exploration of the region, including those of the Government Land Office, Pacific Railroad Surveys, Stansbury, Fremont, Nicollet and others, It is one of Hayden’s earliest and most distinctive large geological maps with the Black Hills shown as a brightly colorful "bull's eye," surrounded by pastel shaded tertiary formations. The map also provides excellent detail of railroads, including the Union Pacific, and dozens of forts and Indian ranges. The color key to the right of the title identifies eight different geological formations. The quarto-sized fold panels distinguish this edition from Hayden's "Final Report of the United States Geological Survey of Nebraska" of 1872, which contained the same map but with octavo-sized fold panels.

References: Marcou & Marcou #626.

Condition: B

Backed with linen to repair some minor loss and wear along the folds. There is also a repaired hole at lower right with some minor loss of image with a portion of image in facsimile.