CA 10 to Santa Ana

[Max Rockatansky]

I've been working on a blog for CA 10/CA 42.  That being the case I stumbled upon something interesting; CA 10 originally followed LRN 174 all the way to Santa Ana.  I noted on the 1940 DOH Map there is a multiplex of US 101 Bypass/CA 10 on Firestone from CA 19/Rosecrans to Santa Ana but it becomes just US 101 Bypass on the 1942 edition. 

I couldn't find anything to reference the creation of US 101 Bypass for Los Angeles-Santa Ana in the AASHTO Database.  Obviously it came into existence sometime circa 1938-39 but the lack documentation is really surprising. I was under the impression that US 101 Bypass was tied to the extension of Anaheim-Telegraph Boulevard which later developed into the Santa Ana Freeway corridor.  Does anyone have additional insight into when US 101 Bypass first became a thing and consumed much of CA 10?

Below are the references I'm looking at:

The original definition of CA 10 in the August 1934 California Highways & Public Works:

https://archive.org/details/californiahighwa193436calirich/page/n287/mode/1up?view=theater

CA 10 following the entirety of LRN 174 on the 1938 DOH Map:

https://www.davidrumsey.com/ll/thumbnailView.html?startUrl=%2F%2Fwww.davidrumsey.com%2Fluna%2Fservlet%2Fas%2Fsearch%3Fos%3D0%26mid%3DRUMSEY~8~1~239588~5511892%26sort%3DPub_List_No_InitialSort%2CPub_Date%2CPub_List_No%2CSeries_No%26bs%3D10

The 1940 DOH Map showing the multiplex of CA 10/US 101 Bypass on Firestone to Santa Ana:

https://www.davidrumsey.com/ll/thumbnailView.html?startUrl=%2F%2Fwww.davidrumsey.com%2Fluna%2Fservlet%2Fas%2Fsearch%3Fos%3D0%26lc%3DRUMSEY~8~1%26mid%3DRUMSEY~8~1~239587~5511891%26sort%3DPub_List_No_InitialSort%2CPub_Date%2CPub_List_No%2CSeries_No%26bs%3D10

The 1942 DOH showing US 101 Bypass as the sole highway on LRN 174 from CA 19 to Santa Ana:

https://www.google.com/url?sa=j&url=https%3A%2F%2Fwww.davidrumsey.com%2Fluna%2Fservlet%2Fdetail%2FRUMSEY~8~1~239584~5511889%3A-Verso--Road-Map-of-the-State-of-Ca%3Fsort%3DPub_List_No_InitialSort%252CPub_Date%252CPub_List_No%252CSeries_No%26qvq%3Dq%3Acaltrans%25201942%3Bsort%3APub_List_No_InitialSort%252CPub_Date%252CPub_List_No%252CSeries_No%3Blc%3ARUMSEY~8~1%26mi%3D1%26trs%3D2&uct=1626524451&usg=cf7XlwlzRGw6qqrpgyXxDmrW77E.

[Max Rockatansky]

As an aside I am aware the extension of Manchester/Firestone was completed in early 1937 east of Rosecrans.  The May 1937 CHPW expounds on the project but does not reference CA 10 nor US 101 Bypass.  My assumption is that this is the origin of US 101 Bypass but it is not reflected in the 1937 AASHTO Database scans:

https://metroprimaryresources.info/this-date-in-los-angeles-transportation-history/april/april-30-this-date-in-los-angeles-transportation-history/

[mrsman]

An interesting qn.  Too bad I don't have a definitive answer.

Here's an old post that touched on some of the issues, but from a slightly later time frame.

https://www.aaroads.com/forum/index.php?topic=23727.msg2425478#msg2425478

If I had to guess, it seems that the original routing of US 101 was along Beverly Blvd through the heart of Whittier's business district.  A later bypass took US 101 down Whittier Blvd instead.  This was especially feasible once the 6th street bridge was first consructed.  Meanwhile, CA 26 formed a route following Olympic and Telegraph to Fullerton and CA 10 followed Manchester to Santa Ana.

At some point, the bypass routing was created, probably to relieve traffic in Whittier.  Manchester was great for that purpose, since it's a straight arrow route largely following the SP RR corridor.  However, Manchester passes about 6 miles south of Downtown LA.  So it seems that there was a plan to construct a street in Downey to connect Manchester/Rosecrans with Telegraph/Lakewood, but in the meantime the bypass routing followed with turns down Lakewood between Manchester and Telegraph.  This street was never built, but its routing was largely adopted by the SA Fwy, years later.

So it seems that the bypass corridor, once created, took over much of the eastern portion of CA 26 and all of the eastern portion of CA 10.  This route was feasible once US 101 itself followed Whittier, with a jog along Indiana and Lakewood to make all the connections work.  US 101 bypass was not retired until well in the freeway era.

looking back at the old thread, it seems that a lot of the designations changed very frequently in the 1930s.  I.e. every few months.
US 101 was routed on many corridors before the freeway routing was finalized.  It is likely that the large number of routing changes in this era was simply too numberous to be transcribed onto maps.  It is also likely that once Bypass 101 was signed on a routing, the routing multiplexed the old routing (26 or 10) for a while so that drivers can get used to the change.