500 EMMONS AND MERRILL SKETCH OF LOWER CALIFORNIA. 



It is only within comparatively short distances of the present coast- 

 line that narrow and deep canyon-like ravines are found, the interior 

 valleys being generally broad and shallow, with very indistinctly out- 

 lined stream beds. 



For purposes of geological description the region examined may be 

 divided into the coast or mesa belt, the western range, the interior valley, 

 and the eastern range. The immediate Gulf coast was not visited.* 



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 aggregated clayey sands, sandstones and conglomerates 

 of which the lowest horizons carry characteristic forms of the Chico-Cre- 

 taceous. 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° 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 protect- 

 ing the softer beds from erosion. 



The best exposures of the lower beds were found between Canoas and 

 Bluff points (see plate 19), where they present perpendicular bluffs, 

 facing the sea, from a few hundred up to nearly a thousand feet in 

 hpight. These are being rapidly undermined and eaten back by the 

 action of the waves, so that between the two points the coast-line forms 

 a bow-like reentering curve, set back 3 to 5 miles from a line drawn be- 

 tween the points. From either point the land rises in a series of steps 

 or broken terraces to an extensive plateau, cut on the sea faces by short, 

 narrow, branching ravines and presenting in general continuous bluff 

 faces inland. 



Midway in the reentering curve between Canoas and Bluff points is 

 the Playa Santa Caterina, where is a gap a mile or two in width between 

 the bluffs bordering the ocean, formed by a broad valley in which are 

 two modern stream beds draining the interior region. They are divided 

 at the shoreline by a flat-topped ridge of Chico beds, near the top of 



*0n plate 19 is given a generalized section across the peninsula on a line running approximately 

 from Playa SantaCaterina through the onyx quarries. 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 approximation to nature as the data would admit. 

 Distances were estimated in travelling to and fro and checked by rough triangulations made 

 with a prismatic compass. The vertical scale is intended to be about four times Inrger than the 

 horizontal. 



