1914] Sumner, et al.: Physical Conditions in San Francisco Bay 75 
We should also have expected that the period of least salinity 
would lag behind that of the greatest rainfall, and this relation is 
apparently indicated by our diagram. We must remember, however, 
that we have no record of the salinity of the bay between February 
and April. The actual minimum for the year may have occurred at 
some distance from the point indicated. 
The following table gives the mean rainfall for each month of the 
year at each of the three points above referred to, based upon many 
years’ records of the United States Weather Bureau. It is likely 
that these figures may be of interest, in comparison with those upon 
which our curve is based, representing an exceptionally dry season. 
TABLE 19 
RAINFALL AT THREE PoINTS REPRESENTING REGIONS TRIBUTARY TO 
San Francisco Bay 
Red Bluff San Francisco Fresno Mean for 
Mean of Mean of Mean of the three 
Month 31 years 62 years 30 years points 
July 0.02 0.02 Trace 0.01 
August 0.03 0.02 Trace 0.02 
September 0.69 0.30 0.29 0.43 
October 1.44 1.01 0.63 1.03 
November 3.07 2.55 3 2.25 
December 4.61 4.56 1.47 3.55 
January 4.49 4.90 1.71 3.70 
February 3.76 3.55 1.36 2.89 
Mareh 3.73 3.78 1.81 Sal 
April 1.85 1.67 0.57 1.50 
May 1.27 0.73 0.56 0.85 
June 0.47 0.16 0.11 0.25 
Total 25.43 23.25 10.04 19.59 
! ! ! | | je 
Apr. May Jun Jul Aug Sept Oct. Nov. Dec. Jan. 
Feb. Mar. 
Fig. T. Variations in the regional range of salinity during an annual 
cycle. The ordinates represent the differences between the highest and lowest 
salinities occurring simultaneously in the bay at any given time of the year. 
Jan. 
Figure T represents the regional range in salinity throughout the 
annual eyele. It is quite intelligible that the greatest extremes were 
