Most of my sources come from materials I've purchased on eBay. One of the best books I've purchased was "It Started In The Mountains"
available from the PSIA for aprox. $20.  Lowell Skoog has a nice site (Alpenglow) documenting much of the mountaineer history in the PNW.
(link below)

Sources:  (last updated 3/17/2004)

*1947 Sportsman's Guide for Washington
*1949 Sportsman's Guide for Washington
*American Ski Annual (I've purchased various years ranging from 1941-1951 and still searching for more)
*Snoqualmie Pass, from indian trail to interstate (available at the Snoqualmie Pass Info. Center)
*It Started in the Mountains (available from PSIA)
*The Colorado Skier (He collects information on old ski areas and other misc. ski related stuff)
*Ski Washington  1963 Tourist Promotion pamphlet for WA ski areas.
*USDA Forest Service Recreation, Winter Sports Report for 1947-1948 season.
*NorthWest Ski Trails - Put out by the Mountaineers in 1968
*Alpenglow Ski Mountaineering History Project
*Yakima Valley Regional Library
*Milwaukee Road Employee Magazine - 1939
*NorthernPacific Railroad History Museum