TO -UNCTION OF OK AN I) AND GREEN RIVERS. 65 



o h a. :p t E R I V 



GEOLOGY OF THE ROUTE FROM SANTA FK TO THE SIERRA LA 



PLATA. 



Structure of the valley of the Rio Grande—The valley of the Ohama— Abiqutu- 

 Ooppeb mines— Fossil plants— Ruins of Los Canones— Abiqutu Peak— Plateau 



COUNTRY BORDERUNC THE OPPER OHAMA— ARROYO SEOO— TRIASSIO MARLS— KAVAJO 



Spring — Cretaceous sandstones and plateau— Banks of the Nutria— Middle Cre- 

 taceous beds— Vada del Ohama— Section of valley of the Ohama— High mesa 

 of Upper Cretaceous rooks— Lacuna de los Cavallos— Divide between the 

 waters of the Rio Grande and San Juan— General view of the structure of 



THE SURROUNDING COUNTRY— MOUNTAIN CHAINS— BELT OF FOOT-HILLS— TABLE LANDS— 



Rio Navajo— Oerro del Navajo— Sierra del Navajo— Rito Blanco— The Pagosa— 

 Sierra San Juan and associated mountain ranges — Cretaceous rocks and fos- 

 sils— The Piedra Parada — Rio Piedra— Broken mesa — View from high divide — 

 Rio de los Pinos— Sierra de los Pinos— RlO Florido — VALLEY OF the Animas— 

 Ruins on the Animas— Crossing of the Animas— Structure of the mountains 

 drained by the animas — rlo de la plata — delightful camp — cretaceous rocks 

 and fossils —Sierra de la Plata— Metalliferous veins of the Sierra de la Plata. 



VALLEY OF THE BIO GRANDE. 



The structure of the Rio Grande Valley seems to be essentially the same 

 throughout its entire extent — that is, as far as it is really a valley, viz., from its 

 northern extremity to El Paso. Throughout all this interval it is a synclinal 

 trough, lying between imperfectly parallel ranges of mountains. At El Paso the 

 river breaks through its eastern wall, and, thence to its month, follows a devious 

 course determined by the local obstacles which it meets, no longer modified by the 

 meridional topography of the Rocky Mountain system. Opposite and above Santa Fe 

 the trough in which the river flows is hounded on the east by the lofty ranges of the 

 Santa Fe Mountains and their northern representatives, which extend in an unbroken 

 series to the Parks; on the west, immediately opposite Santa Fe, by the hold and 

 picturesque chains of the Valles. These mountains have but a limited extent, falling 

 off suddenly on the north, and leaving a low pass, which is traversed by the Chama. 

 North of the (mama they are succeeded by the mountains of Conejos, which conned 

 with the wide-spread and tangled maze of high sierras, to which I have referred in the 



OSF 



