The following is an excerpt from History of San Mateo County California by Roy W. Cloud published in 1928. This chapter in turn was written by George A. Elliott, Vice President and Chief Engineer of Spring Valley Water Company at the time of its original publication in 1925:

The year 1864 is notable in Spring Valley annals. It was then that a young man left the draughting-room of the Vulcan Iron Works to become assistant engineer for the water company. This was Hermann Schussler, who had been graduated in engineering in Zurich, Switzerland. He was destined to exert a profound influence upon the development of San Francisco’s water supply. A. W. von Schmidt had been Spring Valley’s first chief engineer. Calvin Brown succeeded him, and to Brown, who was constructing a new dam at Pilarcitos, young Schussler reported.

Hermann Schussler’s first distinctive achievement was the discovery of the reservoir possibilities of San Andreas Valley, northeast of Pilarcitos, and at a lower elevation, in San Mateo County.

“While making the survey for the Pilarcitos pipe-line,” Mr. Schussler said many years later, “I noticed, while running one trial line up the San Andreas Valley, some level ground, and I changed the route of the pipe-line and laid it on the hill toward town, and we built the pipe-line on this second line. But I kept my old notes of the valley line and found for a distance of nearly three miles that this valley raised but very little, perhaps ten or fifteen feet. So, I kept this in mind, and when, gradually, the daily demand for water increased, I asked the executive committee of our board to go out with me and take a look at this valley, privately, in such a way that we wouldn’t be recognized by those eagle-eyed farmers. … They made up their minds that there was something in it. So, they set an agent to work, and bought up this valley, with most of the watershed – another four or five miles.” The damming of San Andreas Valley began in 1868.

The entire chapter can be accessed via the following link:
http://www.waterworkshistory.us/CA/San_Mateo/1928SpringValley.pdf