This was an impossibly difficult location to find and without the help of that certain unnamed source, I'd never have found it. I had deduced it was in the same immediate area as The Timber Falls Motel, Easter Park, Johnson Residence, One Eyed Jacks, etc..., but the vegetation was so overgrown and the homes so tucked back from the road that it was terrifically hard to spot them while driving by.
Naturally, the main thing I was looking for to identify the location from the road were the elaborate wooden fences at the entry to the the property, but as I later realized, they were built for the show and had since been torn down. They really went all-out making these houses appear more woodsy; applying wooden trim to all the windows, doors, etc. Below, the windows that Harold looked out of to see Donna walking down the path and an example of the wood trim they put around the house.
When they came back to the location to shoot a scene for episode 16, they had to rebuild the wooden fences, this time changing the design a bit by using a curved log above the entry instead of the straight one we saw in episode 9.
All interior scenes of Harold Smith's house and the "exterior" scene seen below, were shot on sets built to replicating the original location. They did a damn good job!
All we ever see of the exterior of the Tremond/Chalfont house is this door, which is actually the back door of the house... and in typical Southern California fashion (see Leo and Shelly's house), there's a washer and dryer outside just to the left of the door.
The front of Harold Smith's house, which is never seen in the series, was actually filmed to be used as the exterior of the Briggs' residence. I guess they decided that it didn't look enough like the Pacific Northwest and scrapped the idea. I think they made the right decision.
Below are some other photographs I took of the property; the front of the Tremond/Chalfont house, the path Donna walks down, Harold Smith's door, and the mailbox Donna and James stand next to the night Harold catches Donna and Maddy trying to steal Laura's diary.