TO JUNCTION OF GRAND AND GREEN RIVERS. 53 



CH A P T E R III. 



GENERAL VIEW OF THE GEOLOGY OF THE COUNTRY BORDERING. 



THE UPPER COLORADO. 



Bl EDS-BYE VIEW OF THE COLORADO PLATEAU AND ITS SURROUNDINGS — MOUNTAIN CHAINS 

 BY Wllieu THE PLATEAU IS ENCIRCLED — KOOKY MOUNTAIN SYSTEM — ITS EXTENT AND 

 GENERAL STRUCTURE — DlFPEKENT FEATURES "WHICH IT PRESENTS on DIFFERENT PARAL- 

 LELS—DIFFERENT RANGES OF THE Kooky MOUNTAINS PROBABLY NOT OF THE SAME 



age — Kooky Mountain region eias suffered alternations of elevation and depres- 

 sion — The Cretaceous epoch an era of subsidence — The Tertiary of elevation — 

 MogolIiOn Mountains probably not a distinct system — Mountains of the Lowes 

 Color ados a part of the Sierra Nevada system — Relations of thk Sierra 

 Nevada to the Rooky Mountains — Cerbat Mountains — Wasatch .Mountains — San 

 Francisco group — Recent volcanic phenomena of the great central plateau — 

 Mount Taylor — Sierra Tucane— Sierras Abajo, La Sal, etc. — Structure of the 



Colorado PLATEAU— DEVONIAN AND SILURIAN BOOKS OF THE (iRKAT CAfifON— CARBON- 

 IFEROUS FORMATION — TRIASSIO AND CRETACEOUS ROCKS — SIMILARITY OF STRUCTURE OF 

 THE VALLEYS OF THE LITTLE COLORADO, SAN JUAN, GRAND, AND GREEN KlVERS — 

 II Kill MESAS OF NAVAJO COUNTRY AND UPPER SAN JlJAN. 



A brief description of the general features of the structure of the country border- 

 ing the Colorado will be a necessary introduction to the more detailed analysis of the 

 geology of the region west of the Rio Grande, explored by the San Juan expedition. 



The country bordering the San Juan forms a part of one great geological district, 

 of which the structure, though not alike throughout, considered in its totality, exhibits 

 a remarkable symmetry. This district I have in part described in the fifth chapter of 

 m v report to Lieutenant Ives, and have designated bv the name of the Basin of the 

 Colorado. It is, in fact, geologically a basin; topographically, a great plateau. Could 

 one be elevated to a sufficient height over the center of this region, and be erifted with 

 superhuman powers of vision, he would see beneath him what would appear to be a 

 great plain, bounded on every Bide by mountain ranges, and here and there dotted by 

 isolated mountain masses, rising like islands above; its surface. lie would see, too, the 

 profound chasm of the Colorado CafiOll scoring with tortuous and diagonal course the 

 plain, throughout the entire length of its greatest diameter; for nearly five hundred 

 miles the stream flowing from 3,000 to 6,000 feet below the general level, and at all 

 points bordered by abrupt, frequently perpendicular crags and precipices. Most of 

 the surface beneath him he would perceive to be arid and desert-like; barren wastes 

 of rock and sand; nowhere continuous forests or carpets of herbaceous vegetation; 



