Do you remember if the nickname was "Orange Book" or was it "phone book"? I didn't see the former when searching for more information, but the latter was referenced here [0].
If it's actually "phone book", then [1] seems promising.
It looks like the "Assembly Language Handbook" in the first reference. It was a very thick book, printed on very thin paper like a phone book. I clearly remember it as "Orange Book", after all, it is orange, but that just might have been Caltech vernacular. (Caltech had many local words unheard off campus.)
A marvelous find, thanks! I'm glad they haven't all vanished. I'd still like a scan pdf!
If it's actually "phone book", then [1] seems promising.
[0] http://www.columbia.edu/cu/computinghistory/pdp10stuff/
[1] http://www.bitsavers.org/pdf/dec/pdp10/TOPS10/1972_PDP-10_Us...