U.S. Route 80 (US 80) was a U.S. highway in California that continued east across the country to Georgia. The western terminus of US 80 was in San Diego, California, and it continued east through the city on several different alignments through the years. The highway went through the Cuyamaca Mountains, encountering many switchbacks, before descending to El Centro. After passing through the sand dunes, the highway crossed the Colorado River into Yuma, Arizona.
The highway replaced a 1912 plank road across much of Imperial County. The winding two-lane road through the Cuyamaca Mountains was one of the factors that led to a four-hour journey from San Diego to El Centro. During the 1930s, the road was realigned through the mountains, but several curves remained. In the 1950s, work began on constructing what would become Interstate 8 (I-8) to replace the old highway in San Diego to bypass the cities of San Diego, La Mesa, and El Cajon. This started with the construction of the Alvarado Canyon road as well as Mission Valley Road through the San Diego area, as well as construction of a replacement for the old highway across the Viejas Grade. The construction continued across the rest of the route through the next two decades. US 80 was gradually decommissioned after 1964 as I-8, through San Diego and Imperial counties, was completed. In 2006, the highway was designated by the California State Legislature as Historic U.S. Route 80.
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