|The blue arrow is the location of the Tunnel Rock quarry; the red arrow is the reported location of the Kaiser Sand & Gravel quarry. The pink camera icon is where I actually took the photo.
First off, let me congratulate the searchers! Ramón, Rosemary, Maca… you’re doing great work!
Like Hans, I also wrote to Steve Edwards—he also told me that he wasn’t really a historian. A great guy, but he didn’t really know when the quarries operated.
As several people pointed out (I think Ramón was first)—there is a great collection of the papers of Henry J. Kaiser at the Online Archive of California (OAC.cdlib.org). http://www.oac.cdlib.org/findaid/ark:/13030/tf2v19n6d0/entire_text/
If you search, you’ll find that Kaiser Sand & Gravel began in 1923, but they had sites in many locations (Santa Barbara,Radum near Livermore, Clayton, Hetch Hetchy (near Yosemite)
And so on…
But then Ramón found ftp://ftp.consrv.ca.gov/pub/dmg/pubs/cg/1956/09_08.pdf with his query:
["tunnel rock" site:ftp.consrv.ca.gov]
In this document from 1956, the Tunnel Rock quarry was explicitly mentioned as having opened “near the east end of the Broadway Tunnel” which is exactly in the Sibley Volcanic Regional Preserve. This document says it was operating in 1954, and that “for the past few years, crushed rock has been produced from the volcanic rocks of the Moraga formation (Pliocene) at the Tunnel Rock quarry in the hills southeast of the Broadway tunnel.” (What we now call the Caldecott Tunnel was once called the “Broadway tunnel” since Broadway ran into the tunnel.)
This makes it sound as though Tunnel Rock opened around 1951 and the Kaiser Sand & Gravel pit opened in January 1954. The text (which I read carefully several times through) makes it implicit that the Kaiser quarry opened then.
As several people pointed out, the tunnel construction started much earlier (1934) and completed in 1937. But the approach to the tunnels needed major improvement, and THAT started in the 1950s. That’s when the Division of Highways started to improve the road leading to the tunnels (Highway 75), upgrading it to a freeway. That would have required a good deal of crushed rock… and that’s when the quarries were opened to provide crushed volcanic rock for road construction. (See: http://www.caldecott-tunnel.org/index.php/project-overview/history-caldecott )
And I still haven’t made it over to Stanford library to check out that book by Steve Edwards. But if his email is any indication, I bet there’s not much in it to answer our questions.
Search lessons: First off, the willingness to stick-with-it and learn from other people's searches... that's a key lesson. The idea to search at Consrv.ca.gov was a great idea.
Also, sometimes a social network is what you really need. Thanks for pitching in and making this a great search problem! (And solution.)