What was the original northern terminus for CA-9?

[Quillz]

I've got several historical maps of the East Bay, and none of them make it clear where CA-9 has its northern terminus. Most maps (from the 60s and earlier), show CA-9 following what is today CA-238 from Irvington to Hayward. At that point, it's unclear. There are several highways that, at the time, did not appear to be numbered (I-238, CA-92). My assumption is CA-9 would have still followed what is today CA-238 northward to terminate at what was then US-50 (now I-580). But the maps are unclear... It could have also followed what is today I-238 to terminate at CA-17 (today I-880).

[myosh_tino]

My assumption is CA-9 would have still followed what is today CA-238 northward to terminate at what was then US-50 (now I-580).

You assumption appears to be correct.  According to cahighways.org, CA-9 originally ended at the current 238-580 interchange in Castro Valley...

From cahighways.org...
"Near the mission (at Mission Blvd), Route 9 diverged, continuing signed as Route 9 (but still LRN 5) along what is now Route 238, ending at US 50 (present-day I-580). This was also added in 1909."

[NE2]

http://archive.org/stream/californiahighwa193436calirich#page/n275/mode/2up
"9. Santa Cruz to Milpitas, via Redwood Park."
The map implies that US 101E still existed between San Jose and Hayward, so SR 9 ended at the intersection of Serra Way and Main Street (then US 101E and SR 13) in Milpitas.

Soon after, US 101E disappeared, and SR 9 was extended north to replace it. It overlapped SR 17 (former SR 13) north to modern SR 262 at Warm Springs, overlapped SR 21 on Mission Boulevard to the modern I-680/SR 238 junction, and then followed modern SR 238 to US 50 (now I-580) in Hayward.

[DTComposer]

http://archive.org/stream/californiahighwa193436calirich#page/n275/mode/2up
"9. Santa Cruz to Milpitas, via Redwood Park."
The map implies that US 101E still existed between San Jose and Hayward, so SR 9 ended at the intersection of Serra Way and Main Street (then US 101E and SR 13) in Milpitas.

Soon after, US 101E disappeared, and SR 9 was extended north to replace it. It overlapped SR 17 (former SR 13) north to modern SR 262 at Warm Springs, overlapped SR 21 on Mission Boulevard to the modern I-680/SR 238 junction, and then followed modern SR 238 to US 50 (now I-580) in Hayward.

It seems as if the Warm Springs-Hayward section was unsigned for a while: US-101E is on the 1934 Caltrans map:
http://www.davidrumsey.com/luna/servlet/detail/RUMSEY~8~1~239596~5511897?qvq=q%3Acaltrans%3Bsort%3ADate%2CPub_Date%2CPub_List_No%2CSeries_No%3Blc%3ARUMSEY~8~1&mi=11&trs=86

Is gone from the 1936-37 edition:
http://www.davidrumsey.com/luna/servlet/detail/RUMSEY~8~1~239593~5511895?qvq=q%3Acaltrans%3Bsort%3ADate%2CPub_Date%2CPub_List_No%2CSeries_No%3Blc%3ARUMSEY~8~1&mi=13&trs=86

That section is unsigned on maps through the 1946 edition:
http://www.davidrumsey.com/luna/servlet/detail/RUMSEY~8~1~239576~5511884?qvq=q%3Acaltrans%3Bsort%3ADate%2CPub_Date%2CPub_List_No%2CSeries_No%3Blc%3ARUMSEY~8~1&mi=22&trs=86

And then CA-9 shows up in 1948:
http://www.davidrumsey.com/luna/servlet/detail/RUMSEY~8~1~239573~5511882?qvq=q%3Acaltrans%3Bsort%3ADate%2CPub_Date%2CPub_List_No%2CSeries_No%3Blc%3ARUMSEY~8~1&mi=24&trs=86

The CHPW map also implies that CA-13 and US-101E were on different alignments north out of San Jose, when they were actually both on Oakland Road (the map implies CA-13 on the Eastshore/Nimitz route which didn't begin construction until the '50s).

[NE2]

The 1936-37 official doesn't show any state routes. But you're right about that road being unnumbered from 1938 until 1948.