Jill Livingston's: "That Ribbon Of Highway"
Mike Ballard's Ridge Route Site
National Register of Historic Places --the ridge route is listed here
US 99 Side Trips: Piru Gorge and Gorman -- this has a little info
Santa Clarita Valley Historical Society
The Ridge Route Communities Historical Society and Museum
Don Wilson's Historic Hwy. 101 site
http://caltrafficsigns.com/ -- Pictures and info about historical traffic signs