Today, a motorist can traverse 66 miles of some of the most difficult terrain in the U.S. in under two hours, through country that once provoked complaints from no less a mountaineer than John Muir. “In the mountains of San Gabriel,” Muir wrote, “Mother Nature is most ruggedly, thornily savage.” And yet the Angeles Crest Highway soars through those same mountains almost effortlessly. Its grade never exceeds 6.5 percent. Few of its curves turn a radius tighter than 300 feet. Within five minutes, it achieves commanding views of Los Angeles. Within 30, pine flats.

The ease of the drive belies the difficulty of the highway’s construction, which began in 1929 and continued for 27 years under the direction of the California Department of Highways (now Caltrans) and the U.S. Bureau of Public Roads (now the Federal Highway Administration). During the Depression, homeless men performed much of the back-breaking work. Later, convicts from San Quentin and Chino took up the shovels and pickaxes and were even permitted to handle dynamite. “Good living conditions and a feeling of accomplishment make the assignments to this highway camp coveted by the prisoners,” engineer John Ritter reported in California Highways and Public Works. “There are no fences, no iron bars and no firearms in evidence, but even so attempted escapes by any of the inmates have been very infrequent.”

Today, hikers and picnickers can drive in to enjoy the warble of a songbird or the rustling of wind through Jeffrey pines. But they are just as likely to hear the distant hum of motorcycles or the wail of CHP sirens.

Engineer J. B. Lippincott, who surveyed the highway for the Automobile Club of Southern California in 1919 (and who had previously surveyed the Los Angeles Aqueduct for William Mulholland), routed it high above the narrow, winding canyons below. It hews to mountain slopes and surmounts ridge crests. Where nature failed to provide a way, workers created one, blasting roadcuts into granite and erecting bridges over drainages. Some cuts are as deep as 240 feet. In the high country near Islip Saddle, the highway tunnels twice through the mountainside. It achieves its highest elevation, 7,901 feet, at Dawson Saddle.

The highway forever changed the Angeles National Forest. The San Gabriels’ so-called Golden Age of Hiking was already fading when work began, and almost immediately after the first segment opened, automotive visitors flooded trail resorts like Switzer’s or forested hideaways like Chilao previously accessible only by foot or horseback. In the 18 months between July 1932 and Dec. 1933, nearly 2.5 million people visited the Angeles National Forest – more than all visitors to California’s national parks combined. As construction extended the road toward Big Pines (which it finally reached in 1956), Civilian Conservation Corps (CCC) campgrounds drew even more visitors deep into the San Gabriels’ remote backcountry. Today, hikers and picnickers can drive in to enjoy the warble of a songbird or the rustling of wind through Jeffrey pines. But they are just as likely to hear the distant hum of motorcycles or the wail of CHP sirens.

The Angeles Crest Highway, seen here in 1934, includes several scenic turnouts as it climbs the Arroyo Seco drainage toward Red Box. Photo courtesy of the Security Pacific National Bank Collection – Los Angeles Public Library.

The Angeles Crest Highway, seen here in a 1934 map, was meant to connect with the San Gabriel Canyon Road to create a scenic loop. The loop was eventually completed but was severed by a landslide in 1978.

Convicts were an essential part of the Angeles Crest Highway construction workforce, but private contractors performed heavy lifting, too. Undated photo courtesy of the USC Libraries – California Historical Society Collection.

The Angeles Crest Highway between Colby Canyon and Red Box in 1934. Photo courtesy of the Automobile Club of Southern Calfiornia Archives.

These photos of construction along the Angeles Crest Highway appeared in the Sept. 1937 edition of California Highways and Public Works, published by the forerunner to Caltrans and digitized by the Metro Transportation Library and Archive.

These photos of construction along the Angeles Crest Highway appeared in the Aug. 1936 edition of California Highways and Public Works, published by the forerunner to Caltrans and digitized by the Metro Transportation Library and Archive.

Since crews began building the highway in 1929, the forces of water, wind, heat, and cold have conspired to undo their work. 1938 photo courtesy of the Pasadena Public Library.

Two highway tunnels, measuring 680 and 470 feet in length, bore through the San Gabriel Mountains high country. 1949 photo courtesy of the Los Angeles Times Photographic Archive, UCLA Library.

The Angeles Crest Highway crosses a remote backcountry once accessible only by a trip of several days on foot or horseback. 1959 photo courtesy of the USC Libraries – Los Angeles Examiner Collection.

1956 photo courtesy of the USC Libraries – Los Angeles Examiner Collection.​