494 EMMONS AND MERRILL SKETCH OF LOWER CALIFORNIA. 



features show considerable analogy with the more northern region de- 

 scribed by Lindgren. The mesa belt proper adjoining the western coast 

 is represented by a series of plateaus from 900 to 2,000 feet in elevation, 

 separated by the deep canyon-like valleys of streams that drain the in- 

 terior. Owing to the soft, crumbling nature of the beds, the escarpments 

 are very abrupt and the topography has something of the character of 

 the Bad Lands of the Great Plains. 



The Coast or Western range is represented b}^ a series of isolated peaks 

 or ridges rising one or two thousand feet above the general mesa level, 

 which are partly connected together by flat-topped ridges baseleveled 

 down to the average elevation of the highest portion of the mesa region, 

 but which in geological structure and composition belong to the same 

 system of uplift as the higher peaks. 



East of this range lie the interior valleys, broad, level or gently slop- 

 ing plains 10 to 15 miles in width and with an elevation above sealevel 

 of 1,800 to 2,200 feet, bounded and traversed by mesa-topped ridges and 

 with occasional sharp peaks rising out of them. These interior valleys 

 all drain to the Pacific through gaps in the Western range and rise gently 

 to the eastward, the same gentle westward slope being noticeable in the 

 mesa-topped ridges. 



On the eastern edge of these valleys, at a distance of about 1 to 15 miles 

 from the Gulf coast, a most sudden change in topographical structure 

 takes place. The broad, level plains, in which the drainage courses are 

 so shallow that their direction of drainage is with difficulty recognizable, 

 give place to deep, narrow, tortuous ravines, descending a thousand or 

 more feet within a few miles of the mesa-topped divide. These ravines 

 wind among a series of sharp, jagged peaks, which evidently are the pro- 

 jecting summits of an older and partially buried mountain chain. The 

 eastern range is represented in part by the summits of this buried range, 

 in part by a series of isolated table-topped mountains rising to an eleva- 

 tion of 3,500 feet, which brings them above the summits of most of the 

 sharper peaks to the eastward. On the immediate Gulf coast is a gently 

 sloping mesa, of varying width, at the base of the eastern range. To the 

 south of the region visited the buried mountains rise still higher than 

 these table-topped mountains and send out spurs to the westward, which 

 apparently cut off the interior valley in that direction. To the north, 

 on the other hand, about 10 miles from the onyx quarries, they do not 

 rise above the level of the interior valley, and the mesa-topped ridges 

 sweep over them, descending in a series of terraces or steps to the Gulf 

 coast. 



The rocks of which this eastern buried range is composed outcrop so 

 frequently in the bottom of the interior valley that it is probable that 



