PHYSICAL GEOGRAPHY 97 



evidence of former extensions and retractions with 

 the advancing and retreating shore hnes and some 

 of them are "drowned" or re-filled estuaries. The 

 courses of the older streams as they cross the valleys 

 are almost buried beneath their own debris, while the 

 upper ends are in V-shaped canyons cut deeply into 

 the edges and surfaces of the rising mountain blocks. 



SUBMERGED CALIFORNIA 



This is a wonderful and but little appreciated por- 

 tion of the State, which borders the Pacific Coast at 

 distances of from twenty to one hundred miles. 



That portion opposite Northern California, which 

 lies north of the Channel Islands archipelago (north 

 latitude 34°) as far, at least, as north latitude 39°, is a 

 comparatively smooth plain somewhat like that of the 

 true Continental Shelf of the Atlantic side. Its uni- 

 formity is not broken by angular relief or relief of 

 any kind, except a few evidences of cross grooves rep- 

 resenting the former locations of now drowned valleys. 



The Southern portion is a belt of submerged land, 

 with its projecting mountain ranges, submerged val- 

 leys and drowned rivers, which have been made known 

 to us by the so-called Sonic Depth Map of the United 

 States Naval Department. Only the highest tips of 

 the mountains are now visible above the surface as 

 islands. 



It is characterized by long, narrow ridges, in al- 

 ternation with deep troughs. These submarine high- 

 lands and valleys, like those of the land, are arranged 

 in, at least, two groups of different ages and directions. 

 (See Plate 1.) 



