I'm recommending some paved trails here, so the OP looking for gravel rides may not be interested. That said, I think the various LA area river trails are a pretty cool thing to check out during an LA visit. LA River, Ballona Creek, Santa Ana River and Rio Hondo all have nice paved trails along their banks and are interesting ways to travel around the LA basin while avoiding motor vehicle traffic. Like the rest of LA, sometimes they can be scenic and sometimes gross and/or disturbing, but river trail rides in LA have never failed to be interesting. Of these my personal favorites are loops involving the San Gabriel LA and Rio Hondo rivers. Loop rides from 25 to 90 miles are possible.
The river rides also have the advantage of being pretty flat, so cranking out lots of miles is reasonably easy. Most of the dirt trails I know about are near the edge of the LA basin and are (a lot) hillier. If you have low gears and/or strong legs then there are lots of options. I know several in Ventura County if the OP is interested (Sycamore Canyon, Sulphur Mountain, etc), but they're all an hour or more away from downtown LA and may not easily mesh with a visit.
Last edited by wayold; 06-11-23 at 07:48 PM.