as for who came up with California's route numbers - one of the old articles (August '34 or Sept '34) might have that info.
I'll check and see. It's kinda interesting that whoever was in an office deciding those numbers back then decided the identity of some of the roads we still have today (namely, major state routes like 1, 49, and plenty of the San Diego-area numbers)!
the thing is, California already has a near-useless set of internal route designations (the LRNs... shudder) so implicitly they recognize that the signed routes are for navigation - so then sign the damn things!
a short form history of the convoluted nature of California route numbering:
1910s - LRNs created, useful in navigation to absolutely nobody
1926 - US routes created, auto clubs start signing them in the next few years
1934 - state routes numbered, auto clubs sign them
1956 - interstates created, I think these were always signed by DOH/CalTrans
1964 - renumbering removes any duplicate US/Interstate situations, theoretically makes state sign routes their legislative #, but introduces such great situations as:
242 (built as 24, signed as 24 until the late 1980s)
260, 112 (signed as 61 thereafter)
164 (built as 19, signed as 19 to present day)
and others over time where a perfectly serviceable road exists on the corridor, but since it is not state-maintained or state-constructed, remains unsigned:
93 (Richmond Parkway/San Pablo Dam Road)
148 (Cosumnes River Boulevard)
258 (Western Avenue)
77 (a myriad of streets from Walnut Creek to Oakland)
87 between 101 and 237
251 (Sir Francis Drake Boulevard)
128 between I-505 and Davis
the north-south segment of 84 between Livermore and Rio Vista
And let's not forget the Route 39 gap between Fullerton and I-10 - in existence in the 1940s, seemingly corrected by 1964, but then reintroduced by the late 1980s AFTER a new improved road was built!?