From there, it head northeast on Downtown San Jose surface streets, roughly following the roads of Oakland Rd, Main St, and SR 238, eventually reaching the present day Interstate 580 (I-580), then east through the cities Pleasanton and Livermore on Castro Valley Rd, Dublin Canyon Rd, and Altamont Pass Rd.

[1][2] US 48 was on the original map of US routes in 1926, running from Stockton to Oakland and San Jose (although at one time it was shown as US 42), along what is nowadays I-580 and US 101E/I-880.

US 48 was largely planned to originate at US 99 in French Camp and travel southwest by way of Altamont Pass to San Jose.

This eventually led to a request by the State of California to the AASHO to extend the east terminus of US 48 to Stockton and create a US 48N to Oakland.

The AASHO rejected this concept but offered an alternative which truncated US 48 from San Jose to Hayward and from French Camp to Mossdale.

The State of California made a request to the AASHO to extend US 50 from Stockton to Oakland in 1931.

The State of California would not attempt to resolve US 101E and the US 99W/US 99E Stockton-Manteca split by pursuing deletion of those routes until 1932.