4 THREE GEOLOGICAL PROVINCES. 



eastern rim of the Great Basin. From the Sierra Madre up to this place 

 the survey followed the eroded valleys of the streams, and the vision WMS 

 bounded on both sides by their high and rocky banks, composed not only 

 of the edges of thick horizontal strata, but often capped with the harder and 

 more unyielding solid lava. The observer as he passes westward from the 

 mountains is thus placed below the general level of the plateau, which does 

 not become apparent to him unless he stands upon the top of the mesas find 

 can thus cast the eye over the whole. The point already reached in the 

 description is about half way between the Sierra Madre and the high mount- 

 ains of San Francisco, and here, as we have seen, the upper strata of the 

 plain are denuded and washed away, so that the banks of the streams are 

 not so high, and the country appears more level or gently rolling. From 

 this place the vision is unbounded toward the north, except by the horizon. 

 The plain stretches far away, without any vestige of a mountain range. 

 Indeed, it is the continuation of this plateau which rises upon the flanks of 

 the Park and Wasatch Mountains at the far north, and through which the 

 waters of Grand and Green Rivers cut their deep canoned channels. Farther 

 south, these streams unite to form the great Colorado, which is also found 

 traversing this grand, plateau." 



Our studies of this great plateau region have not progressed so far that 

 we are able to clearly define its boundaries, but these studies have shown 

 that the region is complex topographically as well as geologically and is in 

 fact composed of many tables; 



In this region the succession of sedimentary strata is unlike any series 

 which has been studied elsewhere in North America ; different groups and 

 different groupings of fossils are found; a different series of unconformities 

 is observed and the displacements by faulting and folding have characteris- 

 tics not commonly observed elsewhere. All these facts seem to warrant the 

 conclusion that this plateau region should be considered as a distinct geologi- 

 cal province, and in this brief report and others which are to follow I shall 

 so consider it. 



A notice of its geographic connection with the surrounding country is 

 needed. That portion of the United States west of the one hundredth merid- 

 ian lies at a great altitude above the sea. The exceptions to this, as immedi- 



