I have been looking on my search engine to figure out what or where the Gold Coast is. Is it that part of Mexico that hangs down from California? Or is it in California?  
The other new boards were easy to spot on a map but I wasn't so sure about this local.  
I am new to the western US and have been making mini trips to Cali to explore.

There's no official definition, but it usually means anywhere along the coast from Los Angeles to San Francisco. Some others might have different end points, or include towns a bit more inland, like Salinas or Ojai. The Gold Coast in Baja is a different story--that's covered by Tijuana.

And I think there is one in Australia, too.

Does it include Lompoc

The Gold Coast of California is the LA - Ventura County line up to Santa Barbara-San Luis Obispo County line.   SLO County is considered to be the Central Coast, and everything North of SLO is Northern California.  LA, Orange County and San Diego are considered to be Southern California.