[3] The route between Pomona and Upland was constructed by the Ontario and San Antonio Heights Railroad Company, which was acquired by Pacific Electric in 1912.

The San Dimas Line was relegated almost entirely to shuttle service between Lone Hill after July 11, 1914, though some through-service to Los Angeles remained until 1916.

[13][12] Rush hour trains continued to serve Covina, and were even rerouted onto new tracks east of Baldwin Park obtained from the Southern Pacific in 1946.

It took several weeks to convert the trolley-activated DC crossing signals to low voltage track circuit operation suitable for non-electrified trains.

Metrolink San Bernardino Line trains utilize the same section in the freeway's median strip; this locomotive-hauled commuter rail service began in 1992.

Directly east of Mission Road the tracks entered a private right of way which ran easterly and then northerly under the Brooklyn Avenue (Macy Street) Bridge.

From Valley Junction (Soto Street and Interstate 10 Freeway), the dual tracks on private way continued east along Ramona Boulevard, through City Terrace, Monterey Park, Alhambra, San Gabriel, and Rosemead to Baldwin Avenue in El Monte.

From that point, the line proceeded east on private way to cross the Rio Hondo on a single track steel girder bridge.

From the San Gabriel River, the line continued east, on private way paralleling Ramona Boulevard, to Badillo Street in Baldwin Park.

[6][16] The San Bernardino Line continued east, on single track on private way, paralleling the Santa Fe Railway north of Arrow Highway, and passing Towne Avenue and Indian Hill Boulevard in Claremont.

It turned east again at Citrus Avenue in Fontana and proceeded north of Arrow Route Boulevard, paralleling it through Rialto toward San Bernardino.

[9][19][20] Electrical substations providing high voltage power were located at Campbell Avenue, Baldwin Park, Baldy View, Etiwanda, and San Bernardino.