Some posters have referred to these docs for specific projects; but Caltrans has them online (mostly PDF) for (almost) every numbered highway. I found links for the districts below:
1: http://www.dot.ca.gov/dist1/planning/regional-system/tcr/
2: http://www.dot.ca.gov/dist2/planning/conceptrpts.htm
3: http://www.dot.ca.gov/dist3/departments/planning/systemplanningTCR.htm
4: http://www.dot.ca.gov/dist4/systemplanning/ctsp_documents.htm
5: http://www.dot.ca.gov/dist05/planning/system_planning.htm#TCRs
6: http://www.dot.ca.gov/dist6/planning/tcrs/
9: http://www.dot.ca.gov/dist9/planning/
10: http://www.dot.ca.gov/dist10/divisions/Planning/advancedplanning/pages/tcrs.html
11: http://www.dot.ca.gov/dist11/departments/planning/planningpages/tcr.htm
12: http://www.dot.ca.gov/dist12/planning/
Transportation Concept Reports (TCR) have superseded the Route Concept Reports (RCR), but some districts have both online, dating from the 1980s through this decade.
Example: in dist 4 there are 1, 4, 9, 12, 13, 24, 25, 29, 35, 61, 77, 82, 84, 85, 87, 92 (no 93), 101, 109 (no 114), 121, 123, 128, 130, 131, 152, 160, 185, 221, 236, 237, 242, 260, 262, 101, and the interstates.
Some reports are not 100% finished (see CA 57 pages: "ROUTE 57 RCR TRAFFIC DATA GOES HERE ! ! !")
Still, seems like a lot of good (sometimes historical) info.
We'll end with a Dave Chappelle meme:
(https://i.imgflip.com/1238fn.jpg)
Caltrans has committed to updating all of the Transportation Concept Reports by next year, IIRC. There's some new guidance being developed on how to put together a TCR and what it should contain. There will be an expanded focus on bicycle and pedestrian access and sustainability, in keeping with the department's new mission and vision and strategic plan.
iPhone
What seems to be a central link page to all districts' TCRs, including for districts 7 and 8 (no links for them in the OP):
http://www.dot.ca.gov/hq/tpp/corridor-mobility/index.html
District 8's reports, especially, are often horribly outdated and/or horribly incomplete. But even those can provide useful historical information, such as on the routing of CA 111 after it was rerouted onto the then-CA 86S expressway, but before other route segments were relinquished to several cities from Cathedral City to Indio.