Wow, I am from this area and I don't recall this story at all. Did OC Register cover it? Looking at the location of the home, not many places nearby where he can get lost, unless he fell in a body of water at a local park there, but it didn't seem that Mr. Harrod had dementia. There is a lot of traffic on those roads throughout the day, so I can see someone immediately reporting an elderly man walking dazed and confused. No disrespect towards LE, but my experience with Placentia PD has not been the best when I had to report elder abuse and identity fraud.
I used to travel on Carbon Canyon/Sleepy Hollow daily for many years and there are lots of hidden areas to pull over. There is also a cult tucked away in the canyon. Carbon Canyon also runs by Carbon Canyon Regional Park and Chino Hills State Park. I am surprised Chino Hills State Park has not been combed for Mr. Harrod. There are hiking paths and rugged terrain. Also, lots of wildlife including coyotes and feral cattle. Hope there are more leads in the near future.