diphthong

i can vouch for a few of the roads around/near lake mathews just east/southeast of corona. a little less traffic and a bit more rural. enjoyed riding some of cajalco rd. (decent amount of traffic but shoulders mostly and good sightlines). lake mathews dr, la sierra ave, el sobrante rd, mockingbird canyon rd, and santa rosa mine rd which are all either surrounding lake mathews or lead to/from roads around the lake. some rollers. some flats, some solid hills but nice winter/spring views. the summer/early fall too hot unless you're done before 11am. just typing this makes me want to hit it soon. it's been a while since i hit that area. not a ton of support around lake mathews but plenty just off the 15 fwy and after mockingbird canyon rd merges with van buren blvd.

if you're considering driving to a destination, redlands (and san timoteo canyon) area to the northeast, lake elsinore are to the south, whittier hills/la habra heights area to the west
and also villa park rd/east chapman ave/jamboree dr/serrano ave/santiago canyon rd area are all a fairly short drive from corona and expand your possibilities.

there's also the norco area just north of corona, east of the 15 fwy, north of the 91 fwy, south of the santa ana river and west of la sierra ave but it's pretty small.
you'd be done with all the roads in that postage stamp sized area within two hours. lots of horses and eucalyptus/pepper trees tho.