Lawson. J 



Post-Pliocene Diastrophism. 



'53 



station. The latter is given in the railway levels at 514 feet above 

 sea level. The .summit of the plateau is thus 1,443 f cet above sea 

 level. It is clear, from the character of the ground, that the sum- 

 mit of the plateau is not the original summit of the delta formation; 

 much has been removed by erosion. Further up the valley, also, 

 these same gravels are known to the writer to be several hundred 

 feet higher than on the plateau near Ties Pinos. The summit and 

 slopes of the plateau are distinctly terraced at various levels. 



In these facts we have all the evidence that could be desired for 

 the conclusive demonstration of (i)the depression of the coast in 

 Pliocene time during the accumulation of the gravels, (2) the great 

 volume of the Pliocene strata, certainly not less than 1,200 feet, (3) 

 the correlation of the San Benito gravels with the Merced series 

 at the lower end of the same valley, '4) the uplift of the valley with 

 its load of gravel, in post-Pliocene time, to an extent not less than 

 the measure of the altitude of the plateau near Tres Pinos. 



Two other facts of interest remain to be mentioned: 1. At the 

 confluence of the Los Meritos and Tres Pinos Creeks, about eight 

 miles above Tres Pinos station, these same Pliocene gravel beds, 

 which, like the " auriferous gravels" of the Sierra, are often firmly 

 cemented, are faulted and thrown into vertical attitudes, clearly 

 showing that the region has been subjected to the action of impor- 

 tant orogenic forces in post-Pliocene time. 2. In passing through 

 the middle or Santa Clara portion of the valley, the valley bottom 

 appears to be a level plain. From its relation to the Bay of San 

 Francisco, and its flat, unterraced surface, one is impressed with 

 the belief that this portion of the valley owes its character to its 

 having been very recently at base-level, a continuation, in fact, of 

 the mud flats of the bay. Assuming this base level origin for the 

 flat, unterraced surface of the Santa Clara plain, we are confronted 

 with the remarkable fact, that the plain is not only not what it 

 appears to be, viz., level, but that it has not a uniform slope. The 

 railway profile which passes through the center of the plain shows 

 a steady upward grade from San Jose, at 86 feet, to Madrone, at 

 342 feet, a distance of 18 miles, or 14 feet to the mile. This is the 

 highest part of the plain, and probably its most level part. Beyond 

 Madrone the grade descends, till at Sargents, 18 miles to the south- 



