Okay, since I have no computer atm (thank god for internet on the phone), I am unable to retrieve a link to a better method than the OOL glitch. So I will try my best to explain it via text.
Welp here goes nothing!
1. Pick ANY canyon race in the quick race map.
Be warned: if you choose any race that is available in career mode, step 4 will NOT work. Example: Lookout Point Canyon Duel crashes the game after the race.
2. Win or lose the race you selected
Just don't click pause and "Return to Main Menu", otherwise - it won't work
3. Go to Free Roam in Career and DRIVE to the race York Road (located in Fortuna)
This is important, because if you "Jump" to the race via map, it won't work. You can set a GPS tho! Just make sure you dont run in to cops.
4. Select the option "Change Active Crew Member"
Don't just go and get the race on when you get there! The game will reset its "race memory"! However, that doesn't seem to happen when you select "Change Active Crew Member". Dunno why, so don't ask.
5. Click pause and then "Return to Free Roam"
You should be left in the canyon after you do so.
6. Enjoy yourself!
Before anyone asks, yes this DOES work with San Juan.