What is “Mountain Cloth?”

I have no knowledge of “mountain cloth” but in the UK and other places woolen pants were often used. This may have been tweed which was used by many early mountaineering expeditions including Mallory’s attempts on Everest.  Certainly a better fibre than cotton for such endeavours.

From what I’m reading, cotton, very tightly woven, which helps repel water.

As you point out, we’re talking 1948, so that makes sense to me.

Perhaps it refers to Ventile cotton fabric

I recall it being the first generation of the classic Nylon/cotton blend and treated with the US army “Quarpel” or similar.

I handled an REI mountain parka of what I am sure was advertised as being constructed from this fabric in the late 1970s

Fabric gets wet but dries out relatively fast, although I did think that the quarpel DWR came out during the 1950s there must have been some sort of water repellent treatment other than alum and soap in 1948

Could just be waxed cotton.  Just a guess.

Doug is on target for the description.

Shnee’s and Martin Brothers Welding sell “mountain cloth” shirts and give details on the fabric.  As for pants, the Kuhl Revolvr cotton pants I’ve had since 2010 are just now showing slight fraying on the cuffs, and a pair of cotton canvas Super Trousers from Cactus Outdoors from NZ have really taken a beating at work for two years and still look like new. Both pants are still water repellent but never have been waterproof.