80 CHARACTER AND VEGETATION OF THE PLAINS. 



able uniformity of elevation, and the valley at its upper limit has an average level of 1,200 

 feet. In the extreme east of the valley it becomes more elevated as it approaches the lofty 

 Sierra Bernardino. The whole of this portion of the plain is less continuously level than the 

 western, being broken into by the extremities of the ranges, which are here slightly elevated, 

 and which rise to a considerable height as they approach Temescula mountain, a lofty granitic 

 mass lying midway between San Bernardino mountain and the shore. These narrow the plain 

 at the N.E. extremity at the same time that they elevate it. Those mountains have between 

 them secondary valleys which pour their little streams into the Santa Anna. The plain as a 

 whole may be divided into two : that whose elevation is from 900 upwards, and that which 

 descends from 900 down to the level of San Pedro. 



In the former would be included the San Fernando valley and the plains of Kikal Mungo 

 and San Bernardino; in the latter would be the plains of Los Angeles, San Gabriel, and Monte. 



This extensive plain is separated from the Santa Clara river valley by the Sierra Susanna, 

 already described, which run into and join the sandstone hills forming the foot hills of the 

 Cordilleras. The elevation of that valley, where it is entered from San Fernando plain, is 

 nearly 1,300 feet, (1,286.) 



Along this uniform slope, averaging 14 feet to the mile from the Cordilleras to the shore, a 

 great diiFerence of fertility might be expected, a diversity of soil and a variety of vegetation ; 

 but it is not so. The diversity of growth is more evinced by the appearance of timber on the 

 streams than by' the growth of grass ; and with regard to the soil, it is an uniform mixture of 

 clay and rolled pebbles, forming a light brown loam, with a considerable growth of vegetable 

 mold in its superficial portion. The soil of the lower plains is finer and more clayey, but one 

 common statement might comprise the soil of the whole plain in its utmost extent, namely : 

 local and defined beds of clay, (modern alluvium,) resting upon a bed of fine conglomerate 

 clay and gravel, (ancient alluvium.) 



In the upper plain, about the town of San Bernardino, near Jurupa, and on the Cajon 

 creek, near the pass, sycamores grow abundantly, near water, with oaks, alders, and cotton- 

 wood ; there the oaks, button-wood, and sycamores increase with the altitude, and are found 

 plentifully on the foot hills, both of Kikal Mungo and San Bernardino. 



The upper plains are much better watered than the lower, partly from more rain falling on 

 the more elevated surface, but chiefly because the rivers as they roll down the valley are 

 gradually absorbed by the porous and sandy nature of the soil, which in places is of great 

 depth. Thus a few hundred yards below the town of Los Angeles, the river, in summer time, 

 ceases to flow, it being mostly removed by infiltration into the subsoil, and partly by evapora- 

 tion from the heat, which, for a few months in the year, is very intense. Indeed, everywhere 

 over the whole region the rain fall, which does not exceed 16 inches yearly, is not sufiicient to 

 support vegetation, and hence, in the upper valleys at San Fernando and at Kikal Mungo, irri- 

 gation by sequias is had recourse to ; and without this system the plains of Los Angeles could 

 not produce the excessive crops of grape vines which they do. In the spring and early summer 

 there is abundant water derived from the melting of snows on the Kikal Mungo and the 

 San Bernardino ranges, which are occasionally retained on tlieir summits to the middle of 

 summer, and supply the numerous arroyos and creeks that find their way into the San Gabriel 

 or Santa Anna rivers ; besides which, the dews which fall nightly in spring are very heavy and 

 are equivalent to a mild rain fall. 



A very fine meadow grass grows in portions of the valley, and the wild oat is common over 



