In the region of the headwaters of the Canadian is embraced a territory which, for the completeness of its geological record and the interest of its concomitant topographical and scenic features, is not excelled perhaps by a similar extent of country in the West. It is bounded on the west by the Spanish range, which in this part of its course consists of a densely-wooded watershed-divide, 9,000 to 11,000 feet in altitude, from which at intervals lofty lateral spurs are thrown off, whose bald summits overtop by 1,000 to 2,000 feet the actual watershed, which latter extends in a general north-south direction. Near the Colorado line, the range is intersected by the Raton Mountains, a range of gladed hills extending eastward forty or fifty miles, and constituting, with the still easterly prolongation in the Chicorica Mesa, the northern limits of the district, which opens out to the southeastward into the great plain. Thus defined, the district comprises an area of about twenty-five hundred square miles.
During the season of 1869, in the progress of his extended reconnaissance of the Rocky Mountains, Dr. Hayden visited this region, from whom we have authentic account of its general geological features, and their intimate relation to those prevailing in other and similar districts to the north and south. A few months' residence in this part of the country in 1874-'75* afforded the writer opportunity to become somewhat familiar with its geological features; and the purpose of the present communication is to present such facts as may tend to contribute something toward a similar knowledge of remote and perhaps hitherto rarely-visited localities, and their connection with already examined districts.