California’s Ridge Route Now Has Bypassed, Flooded and Forgotten Sections

California’s first direct automobile route between Los Angeles and the Central Valley once solved a formidable transportation problem. Today, large sections of the historic Ridge Route are bypassed, flooded or largely forgotten, while Interstate 5 carries the traffic that once had little practical alternative. Yet the road has not disappeared entirely: a 17.6-mile section in Angeles National Forest is documented in the National Register of Historic Places for its statewide significance in transportation and engineering.

The contrast reflects more than the decline of an old road. It shows how quickly a foundational engineering system can become inadequate when vehicle numbers, speeds and expectations change. The Ridge Route opened to traffic as a dirt road in 1915 and was paved with reinforced concrete in 1919, becoming the first commercially efficient paved automobile and truck connection between Southern California and the San Joaquin Valley.

A direct route across a mountain barrier

Before the Ridge Route, travel between Los Angeles and Bakersfield depended on indirect roads that were slow, exhausting and hard on vehicles. The new state highway crossed the rugged mountains north of Los Angeles, providing a direct link between regions that had previously been difficult to connect by road.

Its defining engineering choice was to climb ridgelines rather than follow established canyon routes. Sweeping banked curves and deep road cuts allowed vehicles to traverse the mountainous terrain while avoiding some of the drainage problems associated with canyon alignments. The complete route was approximately 115 miles long, including about 30 miles of new mountain roadway between Castaic and Bailey’s Ranch.

The resulting geometry was suited to the capabilities and traffic of its era, not those that followed. The narrow roadway used hundreds of curves and had a strictly enforced speed limit of 15 mph. Even with the slow operating speed, it represented a major improvement in regional mobility. The route cut 45 miles from the distance between San Francisco and Los Angeles, while motor stages could travel between Los Angeles and Bakersfield in about five hours, compared with eight hours by passenger rail over the mountains.

Success created the case for replacement

The Ridge Route’s usefulness also exposed its limits. Daily vehicle traffic increased from 776 in 1920 to 2,280 in 1925. A road designed for relatively low-speed, low-volume travel had no passing lanes and could not readily absorb the growing mix of automobiles and trucks. Travel times lengthened as demand rose, and the alignment developed a reputation for difficult and dangerous driving.

Engineers modified the road during its operating life. Curves were widened to improve visibility, while some short realignments cut across earlier concrete bends. Roadside businesses provided fuel, repairs, food, lodging and water for overheated radiators. These facilities were part of the operating system required to move early vehicles through an isolated mountain corridor, not merely tourist amenities.

The original 1915 Ridge Route was replaced as the principal thoroughfare in 1933 by the separate Ridge Route Alternate, later designated U.S. Highway 99. The newer road followed canyons and gorges through the Piru Creek area, shortened the trip by about nine miles and reduced travel time by roughly 45 minutes. Its curves had a much larger minimum radius, and its lower elevation reduced exposure to snowfall.

That distinction is essential to understanding the corridor. The Old Ridge Route and the 1933 Ridge Route Alternate were successive roads, not different names for one unchanged alignment. The route of U.S. 99 later formed the basis for the modern highway that opened in 1970 and became part of Interstate 5.

Fragmented, but not entirely abandoned

Interstate 5 displaced the older roads from their original transportation role, but “abandoned” is too broad a description for the entire corridor. Some portions of the original Ridge Route and its successor remain open to traffic. Other sections are accessible only on foot, while broader accounts of the historic corridor identify portions that were bypassed or submerged. Available documentation does not establish the present accessibility or maintenance status of every surviving section.

The National Register nomination captures a substantial surviving piece of the original road. Its 17.6-mile listed segment retains concrete and asphalt roadbed, banked curves, road cuts, culverts, curbing and remnants of roadside inns and a maintenance camp. When documented in the 1990s, 10.5 miles still used the reinforced-concrete surface installed in 1919 as the primary driving surface. Washouts and utility work had reduced structural integrity in several isolated locations.

Preserving an old highway involves more than retaining a strip of pavement. Curves, shoulders, drainage structures, road cuts and roadside facilities collectively show how the system worked and what early automobiles required. On the Ridge Route, those features also record an unusually compressed engineering cycle: a road opened a region, became heavily used, exceeded its practical capacity and lost its main function to two successive highway generations all within little more than half a century.

By Thomas Caldwell — AMI’s senior editor for mechanical and mobility engineering, covering vehicle electronics, systems integration, electrification, chassis systems, propulsion, and safety policy.