All pokemon in this zone are between lvl 40-52, except for larvitar and pupitar, which are lvl 15-20. And magikcarp and goldeen, which are 10-40 with a super rod. Poliwag counts towards the super rod as well.
Outside
Ponyta
Rapidash
Tangela
Ursaring
Donaphan
Arbok
Doduo
Dodrio
Golbat
Poliwhirl
Sneasel
Surfing/Fishing
Poliwag
Magikarp
Poliwhirl
Cave entrance
Golbat
Onix
Ursaring
Donaphan
Larvitar
Magmar
Golduck
Inner cave
Golbat
Parasect
Golduck
Ursaring
Donaphan
Larvitar
Machoke
Misdreavus
Surfing/Fishing (inner cave)
Golduck
Goldeen
Seaking
Magikcarp
Up Waterfall
Golbat
Golduck
Graveler
Onix
Ursaring
Donaphan
Larvitar
Pupitar
Beyond Waterfall
Golbat
Parasect
Golduck
Ursaring
Donaphan
Larvitar
Quagsire
Misdreavus