This road was originally part of the Old Spanish Trail, used by early California explorers and settlers as a stagecoach and trade route linking Los Angeles to Santa Fe, New Mexico. Travel on the original dirt route was arduous, marked by two well-worn wheel tracks, and rain regularly turned it into mud. With the arrival of motor vehicles, a more stable surface became necessary. In 1920, the trail from Los Angeles to San Bernardino was paved 18 feet wide with rigid Portland cement concrete, but within a few years heavy use caused the concrete to fracture and break into sections, harming trade and travel as conditions deteriorated. By 1929, the rigid concrete was resurfaced with bituminous Macadam-type pavement, a predecessor to modern asphalt made of compacted layers of small broken stones with gaps filled by stone, dust, and water; later, a tar or oil-like binder was sprayed on to reduce the blinding dust clouds raised by passing motor vehicles. In 1941, Foothill Boulevard was realigned to its present location and paved with early versions of today’s road asphalt, and this original segment, which had served as U.S. Highway 66, was abandoned for years.
