Completely by accident I stumbled across nicely scanned copies of several issues of Will Thrall's Trails Magazine from the '30s. Just browsing through a few issues there are interesting items including a 1934 map of the trail system in the whole range (not much detail, I'm afraid,) Rev. Rankin's first-person account of his first attempt to climb Monrovia Peak on his birthday at the age of 74, which he apparently continued as a birthday tradition for the next 17 years, lots of ads for mountain camps still operating at the time and descriptions of such topics as ski touring on San Gorgonio and in the Baldy Bowl.
The language is also pretty great. From an entry on "Hiking Correctly, from the National Recreation Association Bulletin with some additions by the editor":
"There's a knack in this walking business that means a lot on nature trips. Watch the good walker with his even stride and how he elevates himself on the balls of his toes... It is best to take a steep hill or mountain at a slow pace as though stepping to slow music. You will soon acquire a sense of rhythm, and then the all-essential measured tread."
At the bottom of the page are links to individual .pdfs for each issue, there are a couple more pages of links that follow as well.
http://trails.lacounty.gov/Documents?page=1#pageTitle
Enjoy!
