SOUTHERN CALIFORNIA ACADEMY OF SCIENCES 7 
The Water and Milk Supply of Los Angeles 
E. lL. LEONARD, B. S., M. D., CITY BACTERIOLOGIST. 
The location of nearly every town of importance in Southern 
California was originally planned by the old mission fathers in 
relation to the possibility of its water supply. The most. im- 
portant missions were built in those districts where water was 
found in largest amount. At these old missions one may see, 
even today, evidences of a high degree of engineering’ skill 
possessed by these people in planning tthe ditches and reservoirs. 
A reference to the map shows that the San Gabriel and Los 
Angeles rivers carry the water from the mountains toward the 
sea, and although not rising directly in the high ranges of the 
Sierra Madre mountains, at least a large part of the rain and 
snow finds its way into these two streams, through the under- 
ground washes with which the San Fernando and San Gabriel 
valleys are filled. The San Gabriel river is different from the 
Los Angeles river in that it has a perennial flow from the 
mountains in which it originates and is less affected by seasons 
of drouth. 
The peculiar geological structure of the washes referred to 
shows they are made up of sand and gravel with the bed rock 
between 200 and 300 feet below the sea level. These immense 
subterranean filter galleries as we may speak of them, make 
the character of our water supply one of the most ideal as far 
as bacterial invasion is concerned. If it were possible to bring 
this water filtered through its beds of sand, gravel and alluvial 
debris directly into our city mains then our water supply would 
be most ideal in quality. 
A study of the differences in the total rainfall in Southern 
California shows great variation, 5.28 inches one year and 38.23 
the next. This necessarily affects the amount of water coming 
through the Los Angeles river, and causes great apprehension 
on the part of those whose business is in any way connected 
with the water supply. 
It is almost incredible that torrents of water coming down 
ravines and canons are absorbed so quickly and disappear 
entirely into the gravel bed of the valley, while the river a few 
miles below shows no inerease in volume whatever. 
Under average conditions the river begins to appear about 
11 miles from West Glendale. Its increase in volume is very 
marked and its flow is about 25 eu. ft. per second at the 
southern bend. At this point the first supply ditch is taken 
out, the water from which is used for irrigating purposes and 
to supply the parks of the eity. 
