- Wintersburg Japanese Presbyterian Mission/Church/Rectory and the Furuta House, Huntington Beach (1910 & 1934) - One of the most important threatened sites in Orange County. I've written a lot about this already.
- Mariner's Medical Arts complex (Richard Neutra, 1963) on Westcliff Dr. in Newport Beach. One of the high-water marks for architecture in Orange County. There are plans to demolish it and replace it with a larger building.
- Ghost Town (1941) at Knott's Berry Farm - The south side of Main Street is still original to 1941. Several other structures are also historically significant. The north side of Main has already been torn down and rebuilt.
- Lighter Than Air Hangars (1942) at MCAS Tustin - One is already slated for demolition. The other appears saved for now, but should be watched.
- Miramar Theater (1937), S. El Camino Real, San Clemente - The theater is on a prime bit of real estate, and developers keep eyeing it and hatching plans for it. (See image above).
- Casino building, Avenida Pico, San Clemente - Recent plans have called for moving, destroying or substantially changing this iconic building.
- Villa Park Elementary School (1919 & 1924) - Still in immediate danger.
- Downtown Yorba Linda - There's not much of a downtown there to begin with. How hard can it be to preserve a couple blocks? Maybe they could just add to what's already there.
- Sam's Seafood (now Kona), Pacific Coast Highway, Huntington Beach - This is one of the last authentic Mid-Century tiki bars and shrines to Polynesian Pop in the country. The land owners (as opposed to the restaurant owners) discussed bulldozing it when the real estate market was hot. That talk has fizzled out, but keep an eye on this place when the market warms up.
- Hobby City (1955-1980s), Beach Blvd., Stanton/Anaheim - Again, it seems the slumping market has delayed demolition - but for how long? This may or may not be considered historic yet - but I have a warm spot in my heart for mom and pop roadside attractions, and this landmark is one of the last ones in Southern California.
- Basler-Twist House (1914), Santa Ana - There's been an effort to save and move it, but it's been executed so badly that I wonder if it will actually survive to see a full restoration.
- Orange County Hospital building (1914), at the UCI Medical Center, Orange - I haven't heard that this will be demolished, but with all the recent expansion, I wouldn't be surprised. This is probably one of the least-known historic buildings on this list.
- San Juan Creek Bridge (1930s), Ortega Highway, just above San Juan Hot Springs - Again, I haven't heard that this is going away, but with all the changes to the highway, it's worth watching.
- Port Theater (circa 1948), Pacific Coast Highway, Corona del Mar - Although the owners seem to have backed away from the idea of demolishing it (which is great news,) their remodelling plan didn't sound like it preserved the historic integrity of the structure. Let's keep our fingers crossed.
- Movieland Wax Museum (1962), Beach Blvd., Buena Park - Less a historic site than a colorful landmark, the museum is now closed and empty. I hope the site's best remaining elements can be worked into whatever replaces it. It wouldn't be hard to save the footprints of the stars in the front courtyard. The same goes for the replicas of Michelangelo’s David (actually a remnant of the Palace of Living Art) and the façade of Mann’s Chinese Theater.
I'm sure I'm forgetting some important sites and buildings, but this is a start. Please post additions to the list by clicking the “comments” link at the bottom of this post.