Wishful Thinking?

John Rucker caught this goof in August 2013 on Bull Canyon Road north of Santa Maria in Santa Barbara County. There were detours in the area due to the widening of the US 101 bridge over the Santa Maria River, also affecting California 166. "US 166" never did exist in California, and California 166 isn't related to the former US 66 in any way.

That said, at one time, US 466 had its western terminus in San Luis Obispo County, next door to Santa Barbara County. Long ago, it was replaced by California 46.