180 MINUTES. 



[May i8 



The line of Suisun Bay, Karquines Strait, San Pablo Bay, and the Golden 

 Gate is the course of the drainage of the Great Valley of California, and the 

 adjacent valleys. It is the natural highway of commercial activity between 

 the interior regions and the Pacific. 



The area of the Bay proper is 301 square miles, of which 83 square miles 

 have four fathoms and more of water; San Pablo at the north has an area 

 of 123 square miles, of which 17 square miles carry over four fathoms of 

 water. 



Both these bays are largely bordered by broad, low, salt marshes, cut 

 by many sloughs. Inside of this marshland (which marks the shoreline of 

 high water) the low, alluvial soil may be from one to six miles wide, to 

 where it joins the foot of the rocky ridges. In places the rocky points reach 

 into deep water. 



Some of these features are well shown on the coast survey chart "En- 

 trance to San Francisco Bay"; and Professor J. D. Whitney's map of San 

 Francisco Bay (1873) will give a general idea of the confining ridges; and the 

 cross breakings. 



There are two features that are particularly noticeable: (i) the sub- 

 ordinate valley running from Bodega through Tomales Bay and Valley to 

 Bolinas Bay. The heights on the southwest side of this narrow valley reach 

 1356 feet in height; and on the northeast reach 1500 to 2604 feet. 



(2) On the prolongation of this valley, across the Gulf of the Farallones, 

 there commences a narrow valley about six miles below Point Lobos, and 

 stretches southeastward, as a line of depression on the east side of the crest 

 line of the Peninsula of San Francisco range, for thirty-six miles in a direct 

 line. In this long stretch lie several small lagoons, and the Cafiada de 

 Raymundo where the Spring Valley Water Company has its main reservoirs. 

 Of course the bottom of this valley is alluvial soil. The water company has 

 two reservoir dams across it, and a third at the exit of drainage through 

 San Mateo Creek or Caiion to the bay on the east. Neither of these dams 

 is reported injured. Professor Branner, of Stanford University, has found 

 some earthquake crevices in the line of depression. No rock rupture is 

 reported there. 



With regard to alluvial soil, it is well to bear in mind the relation of this 

 whether in the valleys or around the bay and ocean shores, and the relation 

 thereof to the rocky base upon which it rests or abuts. 



I was one of the committee of investigation of the 1868 earthquake, and 

 it demonstrated that the course of greatest dislocation at the surface of the 

 ground zvas on the line of contact between the "made" land or the alluvial 

 soil with the rocky stratum. 



This is repeated in this earthquake, and therefore we make a few more 

 remarks upon the bay shore line of San Francisco. 



In the vicinity of the city proper, and within the area of the " City and 

 County of San Francisco" (42.8 square miles), there are several indenta- 

 tions of the shore between rocky points, (i) Buena Cove, where the present 

 " city front " or shipping point lies on " made " ground ; (2) Mission Bay, 

 Creek and Lagoon, being filled in; (3) Islais Creek, farther south. 



