GEOLOGY AND NATURAL HISTORY OF LOWER CALIFORNIA. 075 



range, and that its form was not unlike that of the granite plateau 

 described by Lindgren in the latitude of Ensenada. 



"From Gabb's description it would appear that a similar topograph- 

 ical structure obtains for the part of the peninsula stretching south 

 from latitude 29° to La Paz. The eastern range has for the most part 

 a mesa-topped crest, broken here and there by projecting ridges, which 

 stretch in part across the peninsula and separate the interior valleys. 

 The interior valleys, set oft" successively a little more to the southward 

 and Avestward, become more extensive southward, one being described 

 as stretching from La Purissima to Todos Santos (of the south), a dis- 

 tance of 150 to 200 miles, with an average width of 10 miles. The. 

 western range is aiDparently still more indistinct as a topographical 

 feature and is not recognized by him, but the western mesa region is 

 spoken of as stretching in varying width from Magdalena Bay, in lati- 

 tude 240 30', to Cape Colnett, in latitude 31°." 



(2) GEOLOGY. 



"For purposes of geological description the region examined maybe 

 divided into the coast or mesa belt, the western range, the interior val- 

 ley, and the eastern range. The immediate Gulf Coast was not visited." 

 On Plate 1^ is given a generalized section across the peninsula along 

 the line A-B. Topographical features at some distance from this line 

 are brought in to illustrate the general structure.. Though not drawn 

 to scale, care has been taken to make the section as close an approxi- 

 mation to nature as the data would admit. Distances were estimated 

 in traveling to and fro and checked by rough triangulations made with 

 a prismatic compass. The vertical scale is intended to be about four 

 times larger than the horizontal. 



COAST OR MESA BELT. 



"This area has an average width of 10 to 15 miles, and in it, so far as 

 observed, no older rocks occur than horizontally bedded, loosely aggre- 

 gated clayey sands, sandstones, and conglomerates, of which the lowest 

 horizons carry characteristic forms of the Chico Cretaceous. In a 

 higher horizon of this apparently conformable series a characteristic 

 fauna of the Tejon-Eocene has been found, and in still higher beds a 

 few forms of probable Miocene age were observed. None of these beds 

 show evidence of any considerable disturbance, though in a few 

 instances dips of 10 to 15 degrees and slight displacements with a throw 

 of only a few feet have been observed. They have, however, been exten- 

 sively eroded, and later deposits of post-Pliocene and possibly also of 

 Pliocene age have been deposited upon their eroded surface. Recent 

 eruptive rocks, both acid and basic, have cut through them and in 

 places have been important factors in shaping topographical forms by 

 protecting the softer beds from erosion. 



' From Bull. Geol. Soc. of Am., V, 1894. 



