From The Making of Golden Gate Park, The Growing years: 1906-1950, Raymond H. Clary, 1987:
"The Dutch windmill that had been built near Ocean Beach in 1902 was so popular with the Park Commission that they decided to build another one at the southwest corner of the park. Samuel G. Murphy, a local banker, came forward with $20,000 for the new mill. At a meeting of the Park Commission on June 7, 1907, the members voted to name the new windmill the 'Samuel G. Murphy Windmill,' and a local engineer by the name of Stutt was employed to prepare plans for the new mill at a fee of $300. On August 4, 1907, the plans were approved, and Superintendent McLaren was ordered to begin the construction at once. He was also instructed to estimate the cost of creating a lake that would serve as an irrigation reservoir when the new windmill was built.
"When McLaren reported that the lake could be built for $9,513, the commissioners ordered that the work be done as soon as the weather permitted. Not until April 11, 1908, were the windmill and reservoir completed. On that day Mayor Taylor and his wife, John McLaren and the park commissioners gathered to see the new windmill turn its sails for the first time. The structure pumped from the wells beneath it to the new lake mile away on Middle Drive. In keeping with ongoing political practice, the lake was named after the president of the commission and became Metson Lake.
"According to the Examiner, the windmill had cost $22,000. The Pacific Lumber Company donated the two spars for the windmill. These spars were 2 feet square at the hub and 8 inches square at the tip. they were 114 feet long, and each was cut from a single log.
"W.J. Dingee, the former commissioner, donated 1,500 tons of concrete for the mill and Louis Sloss donated the copper dome.
"The Dutch Windmill, built in 1902, had been covered with cedar shingles, but the Murphy Mill was covered with slate shingles. It is interesting to note that former Commissioner W.J. Dingee owned or controlled most of the slate mines in California."
From the Western Neighborhood projects: Murphy Windmill
Location: Southwest corner of Golden Gate Park (near 48th Ave & Lincoln)
Erected: 1905 (although see below for reports it wasn't finished until 1908)
A gift to the city from banker Samuel G. Murphy, the now sail-less windmill was the largest in the world when it was built. Able to pump 40,000 gallons of well water a day, its purpose was to save the city from the exorbitant costs for Golden Gate Park irrigation water that the Spring Valley Company charged.
The Murphy Windmill had a moment of fame when it appeared in a 1915 Charlie Chaplin movie, "The Jitney Elopement".
Electric pumps replaced the windmill's function fairly quickly and over the years the structure has fallen into great disrepair. For decades, there have been calls to restore the windmill. Currently there is a plan and fund-raising campaign to bring the Murphy back into shape.
An older 2005 story from the SF Chronicle tells of the windmills demise and plans for restoration: Windmills taking a turn for the better.
A most excellent PDF document with picture and history of the Murphy Windmill is available online from Campaign to Save the Golden Gate Park Windmills
If all goes well, the schedule for restoration might possibly be complete at end of 2011!