150 



Adventures in Scenery 



basin of Alameda Creek is on the nearly level floor of Livermore 

 Valley (called also Arnador Valley) . This flat plain was the 

 floodplain of San Ramon Creek before it was beheaded. By 

 stealing the waters that had flowed north to Suisun Bay the 

 drainage basin of Alameda Creek was more than doubled. This 



TAMALPAIS 



SAN FRANCISCO 



122 45' 



SAN MATEO 



12215' 



HAYWARDS 



12200 



Scale 



After A. C. Lawson, U. S. Geol. Survey 



FIG. 47. Outline map showing the limits of the great Fault Blocks and 

 the larger faults. The limits of the major fault blocks are shown by heavy 

 dashed lines; faults by continuous lighter lines (broken in the ocean) . T indi- 

 cates the thrust side of an overthrust fault; U the up-raised side of a fault 

 block; D the down-throw side of a fault block. 



is called "piracy," or the stealing of one stream by another. 

 The broad flat-bottomed valleys of San Ramon and Ygnacio are 

 thus explained. These broad plains mark the lower course of 

 what was a much larger and longer stream. Walnut Creek 



