98 PROCEEDINGS OF WASHINGTON MEETING. 



must be one of the most interesting of the great basins, but the writer lias been 

 unable as yet to visit it. 



Basin of Mimbres. — West of the chain of mountain blocks, including the Floridas 

 and Li is Mimbres-Black range groups on the east, and the Sierra Baca, Pyramid, 

 Hatchet, Burro and Black ranges on the west, there is another vast basin into which 

 drains the river known as the Mimbres and numerous othertypical lost rivers, most 

 of which come from the Mimbres and Black mountains. This basin, with its 

 southern extension the Florida plains, includes about fifty townships, or 9,000 square 

 miles, in the United States, and at least as much more in Mexico. Its surface pre- 

 sents the same level topography and its formation is composed of the same lacustral 

 debris as in the other basins mentioned, ami like them it has a drainage slope 

 southward. 



The northern end of this valley receives nearly all the mountain waters from the 



* 



Black and Mimbres ranges, ami like the Franklin-Hueco basin is characterized by 

 numerous lost rivers. One of these, Los Mimbres, is the most conspicuous of all the 

 lost rivers of the west, and has been the cause of much speculation and wonder. It 

 is a boldly flowing mountain stream until it gets well out upon the plain, when it 

 completely disappears by imbibition and evaporation. 



Probabli Basins oftfa P< cos Valley. — The Rio Pecos, from the mouth of Delaware 

 creek to Pecos city, fifty miles below, and thence to an undetermined point some 

 fifty miles further southward, flows in grits and clays of the typical basin character, 

 which, together with the topographic conformation and well-boring records of the 

 region, lead to the belief that this portion of the Pecos valley is another < Quaternary 

 basin. The escarpment of the Llano Estacado is far east of Pecos city, and the river 

 Hows in a flat or basin some thirty miles wide from Toyah to Quito, which seems 

 entirely unlike a river floodplain. This flat is marked on the east by a high scarp 

 line near Quito, 12 miles east of Pecos city, but inasmuch as theapparent shore-line 

 formations were of the softer Red beds and plains formations, instead of the harder 

 mountain rock like that of the other basins, it is difficult to say, after my brief 

 studies, whether or not it is a true shore line, although I am greatly inclined to think 

 it is. The western shore of this apparent basin is the west of Toyah, against the 

 eastern slope of the Davis mountains. Both at Pecos city and at Toyah numerous 

 artesian wells have been found in this alluvial deposit, whether it be of lake or 

 river origin. 



The Volcanic Areas of eastern Xew Mexico. 



Besides the older eruptive rocks of the mountain proper, large areas of the plain 

 and basins of Xew Mexico and Mexico, though not of Texas, are covered by heavy 

 volcanic flows of lava and basalt hundreds of square miles in extent. In many 

 eases these are accompanied by cinder c< »nes i »r craters ; others are fissure extrusions ; 

 and in still others the sources of the flows have not been determined. These lava 

 sheets are especially conspicuous in the vicinity of many of the ancient basins pre- 

 viously described, and their proximity suggests that there is a close relation be- 

 tween therh. 



The Raton-Las Vegas plateau was originally capped by a vast sheet of basaltic 

 lava, which is still the determinative or initial feature in the elusion of the plain of 

 that vast region, which has been mostly worn away. It still surmounts Fishers 

 peak, south of Trinidad, and the great Mesa de Maya, extending fifty miles eastward. 



