Real photo postcard, 1958. On reverse of card: "U.S. Highway 99, commonly known as the Ridge Route, one of America's busiest highways, between Los Angeles and San Francisco. Photo by Ray Foster".

Highway 99 was carved through the canyons in 1933, bypassing the 18-year-old Ridge Route that connected Los Angeles with Bakersfield. Highway 99 would be replaced in the mid-1960s by Interstate 5.

Ridge Route history by Jerry Reynolds:

Ever since the days of Phineas Banning, General Beale and the Butterfield Overland stage, vehicles made their way out of Los Angeles, through San Francisquito Canyon, down the Grapevine Pass, and then into Bakersfield. The California Highway Commission was formed in 1911, and one of its first priorities was to build a simpler, more direct road through the La Liebre Mountains. That task fell to the man with the unlikely name of W. Lewis Clark.

Frustrated in several attempts to locate an easy way across the stony barrier, Clark, at last, blazed a trail right over the top from the mouth of Castaic Canyon to Gorman. It was called the Ridge Route.

After a year of toil, during which four-horse Fresno scrapers graded hilltops alongside chugging Caterpillar tractors to the tune of a staggering half-million dollars, the Tejon Route, as it was originally dubbed, opened to the motoring public late in November 1915. The Auto Club did a little calculating, finding that in the 36 miles between Castaic and Gorman, there were 642 curves that added up to 97 complete circles. It did cut 60 miles off the road, however.

Even before construction started in 1914, an enterprising businessman by the name of Sam Parsons purchased an acre of land from W.H. Cook fronting the stake line, then threw up a general store that catered to the needs of the workers. Afterwards, "Sam's Place" became a mecca for truckers and the beginning of a new town called Castaic.[...]

While the Ridge Route did not bring permanent residents (to the Santa Clarita Valley), for the most part it did cut down on travel time to the great markets of Los Angeles. One could journey to town and back in a single day — amazing! Then there was the increasing horde of gentlemen clad in long linen dusters with goggles, piloting their chugging, spitting vehicles with names such as Marmon "41," Winton "Six," or Packard ("Ask the man who owns one"). They, their womenfolk, and children might get hungry along the way or need gasoline or automobile repairs. So began a series of what might be called "tourist traps." [...]

The next stop (after Newhall-Saugus) along the Ridge Route would have been Castaic, (and then) there was the Ridge Road Garage, The Tumble Inn, Reservoir Summit, and that splendid establishment in the wilderness known as Sandberg. Local rancher Herman Sandberg provided excellent, guaranteed-fresh steaks at his hotel. Slot machines could also be found there and, in a long, low building out back (known as "The Crib,") feminine companionship was available for weary truckers and lonely salesmen. [...]

In 1933 Highway 99 was carved up the canyons, bypassing the 18-year-old Ridge Route, which was already antiquated.