For whom this may interest here is a filming location of Episode 1974 N°27 S4 E2 "Negative reaction" at 32'08 "- House - 1532W Potrero Rd Westlake - coordinates on Google Earth 34°08'45.21" N / 118° 54'47.58 "W
Thank you for your diligence in tracking these down Ghera.
As an "East Coast Man" as Nelson Brenner would say, I had never heard of Westlake until it was mentioned in "Dawn's Early Light" ("the explosion was heard all the way to Westlake"). I looked it up and it's such a tiny community for the LA area (~8000 people).
And yet, it had at least two mentions in Columbo. :+1: