After logging in on your STRAVA account, click on 'Explore', 'Clubs' and type in something like "Marin County" with cycling ticked as the default clubs to search. At least some of the club members will be listed under the club heading with ride data.
You can narrow your search by club, race team, shop, company/workplace, etc.
If you know a STRAVA athlete's name you can click on 'Explore', Athlete Search' and type in the name to bring up his/her data.
Loops, rides and segments can be found by clicking 'Explore', 'Activity Search' and then keying in a location (such as Marin County, California) and ride type ('Road' in this case). You can also search rides with key words or the ride name, if you happen to know it. Using the keyword "Loop" in your search will pull up mainly loop type ride and modified loops/multiple loops, etc.
In seconds you can pop up route names and mileages that will take some time to go check out all the ones you wish to download. I 'think' you have to be a premium member to download on some of the sites. Someone here will know the exact qualifications required.
MMR offers similar functions using slightly different command names.