SP Los Altos Branch

The arrival of the Southern Pacific Railroad, combined with good timing, excellent location and industrious people, made a fortuitous blend to spark the growth of Los Altos.
When Sara Winchester and her sister, Isabelle Merriman, sold 100 acres of undeveloped ranch land to the Interurban Electrical Railroad in 1906, there was no Main or State street in the area, but that land became the downtown triangle that is now Los Altos.
When rail traffic between San Francisco and San Jose became congested, the SP decided to build a cutoff from Mayfield (part of Palo Alto today) that would intercept the San Francisco-Los Gatos line.
It was named the Los Altos branch, and Paul Shoup (later considered the founder of Los Altos) became assistant manager of the railroad’s municipal and interurban electric lines.
Shoup and local realtors formed the Altos Land Co. and filed a development plan for Los Altos in 1907, which provided for a central business district with 2,000 residential lots.
Indeed, the line was called the Los Altos Branch until 1964, when it was formally abandoned by SP after receiving ICC approval... this despite last minute pleas by the 170 commuters who used it.
The last scheduled commute train to traverse the line from California Avenue in Palo Alto (at one time named "Mayfield") to Los Gatos was on January 27, 1964. Espee GP9 #5894 did the honors on Train #132.
The branch had an ABS signalling system in place from San Jose to Vasona and many wig wags.
FWIW, the "Vasona Branch" (via Vasona Junction) was the name bestowed upon the truncated line after it was cut back, terminating at Kaiser's Permanente facility in the Cupertino hills.
An SP local serviced the Permanente plant from San Jose to Cupertino via the "Vasona Branch" until September 1996. UP still services the line today, but that's not on-topic for SP.
In 1958, Southern Pacific abandoned its trackage from Vasona Junction to Los Gatos.
Ten years later, Foothill Expressway had done away with the portion of the line from Permanente Spur to Mayfield (Palo Alto).

The way I understand it, operations on the Los Altos and Los Gatos Branches went like this.
The passenger locals #129 and #130 operated to Los Gatos until 1958. Then the Los Gatos portion of the branch was torn up.
The passenger run was dropped, and the Permanente Local continued to serve from Bayshore Yard, joining the Los Altos Branch at Mayfield (California Avenue) for a roundtrip to the plant.
About 1963 the Los Altos portion of the branch was abandoned, and the local went through San Jose on what was to be today's Vasona Branch. The Permanente Local was eventually moved to San Jose sometime in the late 1960's or 1970's. Switch jobs continue to operate to Campbell and San Jose
Passenger service between California Ave. and Los Gatos was served by trains 129, 132 and 170.
Equipment was deadheaded to San Jose as trains 192 and 193 until the branch was cut back to Vasona Junction in 1958.
Passenger service then ran California Ave. to San Jose until Jan. 27, 1964. The last passenger train on the branch was a Central Coast Railway Club excursion. Around June the tracks were pulled up between Alta Mesa and Simla. A short section of the branch remained in service out of California Ave. to serve Preformed Line Products, which got occasional loads of steel wire. This short section was in place for many years after abandonment of the Los Altos branch.
Freights operated out of Newhall yard via Campbell to Simla and Permanente. After switching the plant the train continued through Los Altos to California Ave and back to San Jose via the Coast Line, switching local industries as needed.
Around 1970(?) the Permanente started working out of Bayshore for a few years. Since there wasn't much business on the Los Altos line, I don't think there was another local working the branch in the '50s.

The Los Altos History Museum, 51 S. San Antonio Road, is open noon to 4 p.m. Thursdays through Sundays, and admission is free. The museum hold a prototype of the 8-foot locomotive and 4-foot tender used on the line For more information, call 948-9427 or visit www.losaltoshistory.org