Here is a Griffith loop from DTLA, taking the LA river bike path. You can stop at La Columbe for a coffee on the way which is accessible right off the path (literally its on the path):
https://www.strava.com/routes/16414250
Mandeville out and back from Blue Bottle in Santa Monica. There is plenty of parking on San Vicente (towards Santa Monica).
https://www.strava.com/routes/16414539
“TOTS” which is Topanga, Old Topanga, Stunt. (probably more like a 3.5 hour loop)
https://www.strava.com/routes/16414545
There are countless other once as well, but those three are mainstays.