I thought this was interesting. I find pics almost randomly sometimes and just happened upon this one. That Beatty Canyon is unmistakable to anyone who spent time in Azusa Canyon, so when I saw the San Gabriel Power House, I thought that sure looks familiar.
The following picture, titled “Powerhouse in San Gabriel, 1915,” sits at the foot of Beatty Canyon. Now this was 1915, long before anyone I knew who might know of the hydro electric plant. Wikicommons describes it . . .
Power house in San Gabriel, ca. 1915
Photograph of the exterior of a San Gabriel Power House in the San Gabriel Mountains, which supplies electricity to Los Angeles and water for orchards of Pomona Valley, ca. 1915.
Here a mountain stream is diverted and brought through steel pipes to the power houses. Two other buildings are visible at right.
A water conduit running down the mountain side is visible behind the power house. The banks of concrete swale in the foreground are lined with river stones and landscaped with small plants.
That ridge above the power house can also be seen here in this photo of the Foothill Dairy in Azusa.
I am sure that no structural foundations of these buildings remain today. If any did, they would be up on Ridge View Drive, a north and soundbound lane that used to run behind the Foothill Dairy.
There is one hydroelectric plant on the river, located just to the north of Azusa. The original Azusa Hydroelectric Plant was built in 1898 by the San Gabriel Electric Company (which in 1917 was incorporated into Southern California Edison). Power generation began on June 30, with an initial capacity of 2,000 kilowatts (KW). During the early 1900s it was mainly used to power the Pacific Electric (Red Car) and Los Angeles Railway (Yellow Car) systems in the greater Los Angeles area. The plant was purchased by the City of Pasadena in 1930, due to structural modifications needed to accommodate the city’s proposed Morris Dam. A new 3,000 KW plant was built adjacent to the old plant in the 1940s.[114]
The power station is supplied with water via the 5.5-mile (8.9 km) long Azusa Conduit, which draws water from the river below San Gabriel Dam, and runs along the east wall of the San Gabriel Canyon to a point just north of Azusa adjacent to the San Gabriel Canyon spreading grounds, where a 38-inch (970 mm) diameter penstock falls 390 feet (120 m) down the mountainside to the powerhouse.[114][115] Between 1996 and 2014 the plant generated an annual average of 4 million kilowatt hours.[116] The usage of river water for electricity production has been controversial, as diverting water can dry up the channel, reducing fish habitat.[117]
Here is the interior.
Duarte, CA 