San Luis Potosí (city)
East towards Tampico/Ciudad Valles (la Huasteca Potosina)
The #25 bus towards Los Gomez (7 pesos) takes you out of town. (The #11 bus towards Quintas might also get you there.) You'll pass a speedbump and then immediately there's a petrol station on your right. That's where you want to get off. There's another speedbump just past the petrol station, so you should be pretty good to either ask for rides directly or stick your thumb out.