86 PROCEEDINGS OF WASHINGTON MEETING. 



:;. The two great mountain systems which limit the region — the- Ouachita on the 

 north, ainl the Rockies and the basin ranges of the trans-Pecos region and northern 

 Mexico on the west : the first of which (the Ouachita system of Arkansas and In- 

 dian territory i is older than the plains of the coastward incline system against 

 which they were laid down. The second system is composed of the basin moun- 

 tains, which consist in part of the uplifted, folded and crumpled southern rock 

 sheets of the earlier of these plains, i. e., those founded on rocks of Cretaceous age. 



4. Plains laid down against and of later age than the mountain folds and syn- 

 chronous in age with the later formations of the coastal series, including the Llano 

 Estacado, and the lacustral or basin sheets laid down between the mountains and 

 in the erosion valleys of the plains. 



The Raton-Las Vegas Plateau. 



It is the popular conception, founded upon the conditions about Denver and 

 elsewhere, that the structure of the plains of Tertiary and later origin is such as to 

 abut everywhere against and incline away from the mountains toward the present 

 eoasl and Mississippi valley, forming a suitable condition for the transmission of 

 underground waters derived from the mountains. This conception is a mistaken 

 one. so far as northern New Mexico is concerned : for south of the Colorado line the 

 western margin of the plains recedes away from the mountains eastward, and inter- 

 posed between the Llano Estacado proper and the Rocky mountains there is an 

 interesting topographic feature — the remnant of an older plane or Eocene land 

 area, the structure of which dips toward the mountain front. 



For this great region of country in northern New Mexico, lying east of the true 

 Rocky mountains and east of the Llano Estacado. south of the Purgatoire and north 

 of the Gallinas, the name of the Raton-Las Vegas plateau may be used to give dis- 

 tinction from the true Rocky mountains toward the west and the Llano Estacado 

 toward the east. This district embraces the buttes and mesas known as the Raton 

 mountains, the Mesa de Maya, and many other remnants of a former plain, and in 

 addition the subsequent plains of erosion upon which the eminences stand and upon 

 which the Santa Fe railway is built from Trinidad to the Pecos. The cities of 

 Trinidad. Folsom and Las Vegas may be considered as bench-marks along the 

 northern, eastern and western boundaries respectively of this region, while Raton, 

 Springer, Maxwell and other points along the Santa Fe railway between the Purga- 

 toire, at Trinidad, and the Pecos an' located upon it. Its southern boundary is the 

 superb escarpment of the Canadian-Pecos valley, which runs eastward from the 

 Pecos, cast of Pecos, crossing near by to the Texas line. This escarpment, as shown 

 on the topographic map (Corazon sheet) of the United States Geological Survey, is 

 over L,200 feet above the Canadian valley, which it overlooks. 



In traveling eastward from the foothills of the Rocky mountains at Las Vegas 

 hot springs (altitude, 7,01)0 feet) the profile of the Raton plateau east of Las Vegas 

 ascends for 13 miles to the breaks of the Canyon del Agua, where the escarpment of 

 I >akota sandstone of the Canadian-Pecos valley is reached. This is an almost verti- 

 cal descent of 1,200 feet to the ranch at its base, where the Red beds begin. This 

 precipitous wall extends irregularly eastward for 100 miles, forming the northern 

 wall for the Canadian-Pecos valley, in the lowest portions of which the streams of 

 the Canadian and Pecos flow over L,500feet below the summit of the plateau. This 

 valley-plain is irregular in outline and of enormous area. In it the'mountain drain- 

 age of the Pecos and Canadian first approach each other and then separate upon 



