That's easy,petalburg city
after you beat your dad and get surf you go to mauville city and surf at the right side of the city
Peatlburg city
On Pokemon ruby to get surf you need to beat your dads gym (in petalburg) then after wallys dad will come and get you then give you surf.
The Fourth Gym is in Lavaridge City.
it is Mauville gym
the gym is in fortree city and it is flying type gym
petalaburg city
Fortree city.
on mauville city
The town in which the third gym is in on Pokemon ruby is in Mauville City (or town, I don't know which one)
The 6th Gym Leader In Pokemon Ruby Destiny is in Down Pour City
fortee city