Part 1; the history of California State Route 1 in the Santa Cruz-Half Moon Bay corridor
During the early period of the American State of California travel along the shores of Santa Cruz County and San Mateo County was difficult. Prior to the arrival of Europeans a well established Native American overland trail existed over Montara Mountain north of Half Moon Bay. This trail was replaced in 1879 when San Mateo County completed the Half Moon Bay-Colma Road as a stage route. The Half Moon Bay-Colma Road eased access to the community of Half Moon Bay and connected several others (namely; San Gregorio, Pescadero, Swanton and Davenport) via an existing stage road south to Santa Cruz. The general path of the Half Moon Bay-Colma Road over Montara Mountain along with the stage road south to Santa Cruz can be seen on the 1882 Bancroft's Map of California and Nevada.
The coastline between San Francisco south to Santa Cruz ultimately became populated enough that the Ocean Shore Railroad sought to build a line between the two cities. The Ocean Shore Railroad operated from 1905 to 1920 but ultimately was never completed between Tunitas Creek and Swanton.
San Mateo County seeing a need for a better road over Montara Mountain completed what was then known as "Coastside Highway" (now Old Pedro Mountain Road) by 1915 as a replacement for the Half Moon Bay-Colma Road. Coastside Highway traversed Montara Mountain via the 922 foot high Saddle Pass. Coastline Highway carried a far more gentle 5% average grade which made it far easier for the average car to traverse compared to the Half Moon Bay-Colma Road. The opening of Coastside Highway brought even further ease of access of to the communities between Half Moon Bay and Santa Cruz
The original alignment of CA 1 north of Santa Cruz to the San Mateo County line appears on the 1935 Division of Highways Map of Santa Cruz County.