it was formerly part of u.s. route 80, and became a business loop for interstate 8 when u.s. route 80 was decommissioned and replaced by the interstate. it is designated as a historic highway by the state of california. only portions of what would become el cajon boulevard in both la mesa and el cajon were originally part of us 80. during a re-routing through san diego onto park boulevard in 1929, the western portion of el cajon boulevard was added to us 80. the next section of el cajon boulevard added to us 80 was between la mesa and el cajon around 1940. today, most of the latter route from la mesa to el cajon has been overlaid by i-8. the final part of el cajon boulevard to receive the us 80 designation was a small piece between park boulevard and normal street in the late 1940s early 1950s when us 80 was re-routed off park boulevard onto the new cabrillo freeway. us 80 ceased to exist legislatively within california after july 1, 1964.