I've scanned the chapter from the "History of PGE" which talks about developments on the Clackamas.  Thanks to Rob for his help, it is now posted in the "Documents" section of the "Historical Items" page of this website.  https://www.trailadvocate.org/scans/PGEHistoryClackamasRiver.pdf  

One of the things I learned in reading this was that the Oak Grove project was not originally a PEPCO (now PGE) idea, but began as a proposal by the Southern Pacific Railroad to develop its own power supply for the planned electrification of its interurban railway system in the Willamette valley.  PEPCO didn't like the idea of competion and worked out a deal with SPRR to take over the project. Given the need for electricity for PEPCO's railway to Estacada and Cazadero and the SPRR's interurbans, it was streetcars and trains that provided the initial impetus to open up the Clackamas country.  The whole history of PGE's involvement on the Clackamas is quite an interesting story.