Easier said than done. Try mapping this and getting "darn close":

Start at PCH and Topanga Cyn
PCH west
Latigo Cyn north
Kanan Rd north
Mulholland Hwy east
Cold Cyn south
Piuma east
Schueren east
Saddle Peak Rd east
Tuna Cyn south
PCH east
End at PCH and Topanga Cyn

I kid you not it takes me about 2 hours each time (I've tried 3 times and routeslip.com gets an error saving it each time) and it comes up 1-2 miles short and 2000' over on the elevation gain. OK so this has nothing productive to add to the thread, but it was a convenient excuse to rant