Geodude is available in the following areas: Routes 45, 46, Mt. Mortar, Dark Cave, Union Cave, Mt. Moon, Rock Tunnel, The Cliff Cave, and the standard Safari Zone.
Graveler is available in the following areas: Route 45, 46, Victory Road, Ruins of Alph, Union Cave, Dark Cave, Mt. Mortar, Mt. Silver, The Cliff Cave, Rock Tunnel, and the standard Safari Zone.
I don't mean to copypaste from GSC, but Geodude plays almost exactly the same as it did back then. That's not a bad thing though, as Geodude was a rocking force in the original games. An early physical wall with dual STAB that hits most early game Pokemon for super effective or neutral damage.
While Geodude was able to solo the first 4 GYMs with ease in GSC, it is now only able to solo the first 3, as Morty has been buffed thanks to the introduction of abilities from Gen III, and the physical/special split of Gen IV. This is a bit of a metaphor for Geodude's usage, as it will fall a bit shorter than it did in GSC. The introduction of the physical/special split and new stronger attacks puts it in a much dangerous position than before, as well as the buffed up post-game.
This doesn't negate the Geodude line at all, in fact there are more positives going for it. The introduction of new moves plus the buffing up of its teammates can keep it going throughout the entire game.
Gym #1 - Falkner (Violet City, Flying-type): Neither of his Pokemon have Mud Slap, making this an easy win.
Proton (Slowpoke Well): Zubat is handled with Rock Throw, and Koffing despite having Levitate now, can't do much besides Poison Gas.
Gym #2 - Bugsy (Azalea Town, Bug-type): U-Turn doesn't hurt, Geodude will have a field day.
Rival (Azalea Town): Gastly doesn't become a threat yet, as it relies on the physical Lick. Zubat is the same, and Quilava is the only starter Geodude can hope to kill.
Gym #3 - Whitney (Goldenrod City, Normal-type): Female Geodude have a better chance here, negating infatuation. With HM Rock Smash, the battle becomes quicker in Geodude's favor. Though a Rollout or Magnitude strategy works here too. Clefairy is actually the more dangerous of the two, as it could pull out a Super Effective move to kill Geodude.
Rival (Burned Tower): Magnemite is out with Magnitude, this battle is the same as before.
Gym #4 - Morty (Ecruteak City, Ghost-type): Gastly is easily handled. The Haunter with Dream Eater and Hypnosis will be a pain, so prepare Geodude/Graveler with a Chesto Berry beforehand. Gengar's Shadow Ball is an actual Special Attack move this time, which is a bad matchup. The strongest Haunter, is also easily taken out too.
Eusine (Cianwood City): Drowzee despite having Confusion, has a low Special Attack and Speed so it can be picked off. Haunter can be tricky with Hypnosis and Curse, so bring a Chesto Berry beforehand again. Electrode's Thunder isn't going to hit, and can be taken out with Magnitude.
Gym #5 - Chuck (Cianwood City, Fighting-type): There's not enough damage to do before getting killed, avoid.
Gym #6 - Jasmine (Olivine City, Steel-type): Both Magneton are easy with Magnitude or Earthquake, but Steelix can hurt a lot with Iron Tail. It can tank a couple Ground STAB itself, so another strategy is to try Fire Blast, or just switch out for someone else.
Petrel (Team Rocket HQ): All three Pokemon are handled easily with STAB.
Ariana (Team Rocket HQ, tag battle with Lance): Intimidate Arbok will be a challenge, but the Geodude line can kill it back as only Glare and maybe Crunch are genuine threats. Gloom is a solid avoid, as it has Mega Drain. Murkrow is pretty easy with Rock STAB. As for the Grunt, he is easy pickings especially if Lance is handling him.
Gym #7 - Pryce (Mahogany Town, Ice-type): Seel and Dewgong are out of the question, and even Piloswine's Blizzard can kill. Don't bother.
Petrel (Goldenrod Radio Tower): Have a field day, the Graveler line detonates all of the Koffing and Weezing. Be sure to heal a few times, or kill them quickly.
Rival (Goldenrod Underground): Sneasel is new, but not even Icy Wind will hurt Graveler. Rock Smash in turn, OHKOs Sneasel. The rest have unchanged, except for the fact that Haunter now has Shadow Ball and should be avoided.
Proton (Goldenrod Radio Tower): He is a joke, like any other Grunt.
Ariana (Goldenrod Radio Tower): Intimidate Arbok is tricky, but goes down relatively easy to Earthquake. Vileplume is a huge nope, and Murkrow is again an easy picking.
Archer (Goldenrod Radio Tower): The Houndoom family can't touch you, Earthquake away.
Gym #8 - Clair (Blackthorn City, Dragon-type): Each Pokemon has a special attack, it is not Graveler/Golem's time to fight Dragon types yet.
Kimono Girls (Ecruteak Dance Theater): Flareon, Jolteon, and Umbreon can be easily handled. Avoid the rest.
Ho-Oh (Bell Tower, HeartGold only): Extrasensory is the most dangerous move it has, but the Graveler line will at least survive a non-crit. They can in turn, OHKO with a Rock move of their choice.
Rival (Victory Road): Alakazam is new, and another avoid. The rest is the same, though Typhlosion can be a bit troublesome but killable.
Elite Four Will (Indigo Plateau, Psychic-type): Everyone has Psychic, don't try.
Elite Four Koga (Indigo Plateau, Poison-type): While Ariados has Giga Drain, it won't do much with it and will probably be killed by Rock STAB first. Forretress can't do much, but will take a while to kill. Muk is a bit annoying, but goes down to Earthquake easily. Venomoth has Psychic, and thus should be avoided. Crobat is an easy picking.
Elite Four Bruno (Indigo Plateau, Fighting-type): Everyone has a Fighting move, except Onix who is the only safe kill.
Elite Four Karen (Indigo Plateau, Dark-type): Umbreon goes down with gradual Rock Smash attacks, but be weary of Double Team. Vileplume is a solid avoid, with Grass STAB. Murkrow is easy to pick off. Gengar has Focus Blast, and is relatively unsafe with Destiny Bond, so avoid that. Houndoom while scary with Special Attacks, can't kill Graveler/Golem in one hit, but gets killed by STAB in one hit.
Champion Lance (Indigo Plateau, Flying-type): The physical/special split plays in Graveler/Golem's favor here. Gyarados should be avoided and thus, Graveler/Golem should not be first out front for this fight. Aerodactyl is easily handled by Rock STAB, as well as Charizard. The Dragonite with Thunder can only touch you with Dragon Rush, a physical move that Graveler/Golem can tank only once at full health. The Dragonite with Blizzard should be avoided, as it will kill. The strongest Dragonite, Graveler/Golem has a chance to tank and hit back because it has Fire Blast. Notable moves for this fight are Rock Tomb, as it can allow Graveler/Golem to strike first due to the speed drops. Rock Polish works much better in that regard, making it so that Graveler/Golem can use a stronger move right off the bat. That strong move can be Stone Edge, which despite the middling accuracy, has a chance to crit. Graveler/Golem should set up on Pokemon that can barely hit it, such as Charizard and Aerodactyl. Another riskier strategy to try is building up speed so that Graveler/Golem can Rollout on the rest of Lance's Pokemon, hoping it doesn't peter out until the end of the battle. Golem has a much better time here, tanking more hits and being a bit more faster than Graveler.
From this point onwards, you can fight the gyms in any order, though you will need to retrieve the Machine Parts from the Cerulean City gym before you have access to the earlier portion of Kanto. Feel free to anticipate or postpone any battles as needed.
Gym #9 - Brock (Pewter City, Rock-type): While Earthquake would normally destroy this gym, Graveler/Golem is very slow and unlikely to outspeed anything but Graveler. As a safety measure, it is much better to not have Graveler/Golem fight here at all.
Rival (Mt. Moon, optional): As usual, avoid Alakazam, Gengar, and Meganium or Feraligatr.
Gym #10 - Misty (Cerulean City, Water-type): No.
Gym #11 - Lt. Surge (Vermilion City, Electric-type): Raichu and both Electrode go down easily to Earthquake. Magneton as well, but Mirror Shot can hurt a lot. Electabuzz also has Low Kick, which hurts as Graveler/Golem is pretty heavy. A Babiri or Chople Berry should be equipped beforehand.
Gym #12 - Erika (Celadon City, Grass-type): Why.
Gym #13 - Janine (Fuchsia City, Poison-type): Janine grew up, but not as much as the other leaders. Both Ariados, Crobat, and Weezing are handled with mild difficulty. However Venomoth like her father's, has Psychic and thus should be avoided.
Gym #14 - Sabrina (Saffron City, Psychic-type): Everyone has Psychic.
Gym #15 - Blaine (Seafoam Islands, Fire-type): Overheat is a risk, but it only works once. Heal up and continue with Earthquake.
Gym #16 - Blue (Viridian City): The matchup here is unfriendly to Graveler/Golem, both Exeggutor and Gyarados should be avoided for obvious reasons. Machamp has Earthquake and No Guard Dynamic Punch so that's a no-go either. Rhydon while slower than Golem, can take multiple Earthquake attacks due to its HP, and hurt more with its Earthquake. Arcanine and Pidgeot are the only safe kills, but be cautious about Arcanine's Intimidate and Dragon Pulse.
Rival (Indigo Plateau, optional): Apparently he doesn't evolve his Sneasel. This match is the same as the one in Mt. Moon but his Magneton is the same as Surge's.
Red (Mt. Silver): Pikachu is a threat with Light Ball Iron Tail, but a Golem that matches it in level can survive and hit back with Earthquake. Because of Hail, even Snorlax is a threat with Blizzard. Nobody here is a safe kill for Graveler/Golem, even Charizard as it has Blast Burn.
Geodude at Route 46, will start out with Tackle and Defense Curl. Both are mediocre moves although Defense Curl has a niche with Rollout later on. At level 4, Mud Sport can help Totodile but there are really no early Electric types to take advantage of. Rock Polish at level 8 is one of the new moves compared to Gen II, and is essential in boosting Geodude's speed up greatly. Rock Throw at level 11, is your first Rock STAB, and primary weapon against the first two GYMs. Magnitude at level 15 while unpredictable, is still good STAB to hit Electric and Poison types. Self Destruct at level 18 is a no, especially if it is pressed it by accident. Rollout at level 22 is a niche, but unreliable. Rock Blast at level 25 is better than Rock Throw, despite the accuracy drop. Graveler and Golem share the same moves at the same levels. The coveted Earthquake is at level 33, though Geodude can get it earlier at level 29. Explosion at level 38 is the same as Self Destruct, ignore it. Double-edge is good to work with if Graveler/Golem has Rock Head, it is a powerful attack to help with resisted hits. Stone Edge at level 49 is just around the time you fight Lance, and it is very powerful. The higher critical-hit ratio is just icing on the cake.
On the TM side, Rock Smash hits what its STAB can't, and can also lower defense. Dig is outdated, and should be used on someone else. Same with the Earthquake TM, as Graveler/Golem's purpose is to gvie another teammate the chance to use the TM. Return is a better choice than Double-edge given max happiness, but someone else is better off with it. Flamethrower and Fire Blast hit other low Special Defenses and specifically Grass types, but it's a gimmicky concept. Rock Tomb is neat to lower the opponent's Speed, but Rock Polish can do it better. Gyro Ball neutrally hits most Pokemon, and works well if Graveler/Golem is going to play slow. Rock Slide has better accuracy than Stone Edge, but the trade off may not be worth it, as it wastes a TM. Graveler/Golem can't learn Stealth Rock by level up yet, so that is another good option to severely weaken opposing teams.
Regarding Move Tutors, none of them are better than what Graveler/Golem already has. Thunder Punch and Fire Punch are mentioned for their use on Water and Grass types, but that is it.
Physical (Johto): Stone Edge/Rock Blast, Earthquake, Double-edge (Rock Head only)/Rock Smash, Rock Polish
Physical (Kanto): Stone Edge/Rock Blast, Earthquake, Double-edge (Rock Head only)/Brick Break/Fire Punch, Rock Polish
Rollout: Rollout, Defense Curl, Earthquake, Rock Polish
Minimum stats are calculated with 0 EVs, IVs of 0, and a hindering nature, if applicable.
Maximum stats are calculated with 252 EVs, IVs of 31, and a helpful nature, if applicable.
Geodude Line Rankings
What Nature do I want? If you want to take advantage of Rock Polish, then Jolly is the best way to go. Otherwise, Brave or Adamant are also good to use.
Which Ability do I want? Sturdy is not very useful in this generation, so Rock Head is generally better, as it allows to run recoil-less Double-Edge. That aside, there is little difference in the usefulness of both abilities.
At what point in the game should I be evolved? You should be evolved into Graveler by the Morty fight. Golem can be evolved at anytime after Graveler, though the preference of trade evolutions is up to the player.
How good is the Geodude line in a Nuzlocke? Geodude kills it for most of the early game in Johto, but it falls short much earlier by the Morty fight. Despite its shortcomings, it lives on raw power and strategy to help it succeed.
Weaknesses: Water (4x), Grass (4x), Fighting, Ice, Steel, Ground
Resistances: Fire, Rock, Flying, Bug, Poison, Normal