For the next 75 miles (121 km), SR 166 crosses the Santa Barbara/San Luis Obispo county line a total of five times.

West of Maricopa, where it skirts Santa Barbara and San Luis Obispo counties, it is called the Cuyama Highway.

In February 1998, a large storm swelled the Cuyama River and caused it to wash out a section of the highway.

Officers Britt Irvine and Rick Stovall were responding to an early morning call about a truck accident when their CHP cruiser drove off the washed out section.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage.