Geodude is available in the following areas: Routes 45, 46, Mt. Mortar, Dark Cave, Union Cave, Mt. Moon, Rock Tunnel, and Team Rocket HQ. In Crystal, it is also available on Route 33. Graveler is available in the following areas: Route 45, Victory Road, Dark Cave, Mt. Mortar, and Silver Cave.
Geodude is, hands down, the most valuable Pokémon you can ever use in a GSC run. It is available in two different places at the very start of the game -- both Route 46 and Dark Cave -- and instantly provides you with an amazing physical wall which can single-handedly destroy the first four gyms with its dual STAB options. Not only that, but its awesome typing, while giving it double weaknesses to Water and Grass, enables it to pair up very well with any of the three starters. Although it is not quite as physically bulky as its cousin Onix, Geodude has substantially better attacking power and movepool, which makes it the superior option. As you progress in the game, Geodude does tend to become a liability against very powerful opponents such as Chuck's Poliwrath or Clair's Kingdra, but its amazing early-game typing more than makes up for it.
Gym #1 - Falkner (Violet City, Flying-type): You can easily beat his Pidgeotto with Rock Throw, provided you don't get haxxed by Mud Slap.
Gym #2 - Bugsy (Azalea Town, Bug-type): You can easily win with Rock Throw.
Rival (Azalea Town): Just use either Rock Throw or Magnitude and make 'em faint (assuming you picked Chikorita). Please don't send Geodude out against Croconaw or Bayleef.
Gym #3 - Whitney (Goldenrod City, Normal-type): You probably should not risk it with the Clefairy due to the unpredictability of Metronome (it has a good chance of becoming a Water or Grass move), but Geodude can easily beat the Miltank by using the decent Defense Curl + Rollout combo (which does double damage) or by just plain spamming Magnitude. Also, Dig is nice to have just in case you need to offset her own Rollout combo.
Rival (Burned Tower): Use your dual STABs to destroy this guy, except if he has a Bayleef or Croconaw. You should probably stay away from those.
Gym #4 - Morty (Ecruteak City, Ghost-type): Watch out for the stray Hypnosis + Dream Eater or Curse, but other than that you should be fine. Levitate does not yet exist, and Shadow Ball is still a physical move, meaning that Graveler can easily tank several hits from Gengar, which has a rather low Attack stat.
Eusine (Cianwood City, Crystal only): Drowzee is annoying, since it likes to put you to sleep with Hypnosis and spam Dream Eater. You should definitely switch out if it manages to land a Hypnosis.
Gym #5 - Chuck (Cianwood City, Fighting-type): Avoid at all costs. Bad on all possible fronts.
Gym #6 - Jasmine (Olivine City, Steel-type): You can easily defeat her two Magnemites, but don't try to face off against her Steelix. It can wreck your face with STAB super-effective Iron Tail, which, against your Graveler, would have the exact same power as if it used Earthquake. Yeah, bad idea.
Rocket Executive battle #1 (Team Rocket HQ): Clean sweep. Everything hits with physical moves, and they bounce right off Graveler.
Rocket Executive battle #2 (Team Rocket HQ): More or less another clean sweep, although the Executive's Gloom should be avoided, for obvious reasons. Murkrow is a bit gambly, because it has Pursuit and good Special Attack; don't switch back in unless you have to.
Gym #7 - Pryce (Mahogany Town, Ice-type): Please, for the sake of Arceus, do not use Graveler in this battle. It will die. Without doubt.
Rocket Executive battle #3 (Goldenrod Radio Tower): Graveler and Golem are amazing at tanking SelfDestructs, and are also able to prevent them entirely by one-shotting all the Koffings and Weezings with Magnitude.
Rival (Goldenrod Underground): If you chose Chikorita, then you can solo this battle with Graveler (Sneasel may seem like a threat, but it doesn't have any Ice-type moves, and it can only really hit you with Faint Attack, which comes off of its pathetic base 35 Special Attack stat). Don't fight against Meganium or Feraligatr.
Rocket Executive battle #4 (Goldenrod Radio Tower): Another dicey battle, due to Vileplume's Absorb (which still hits like bricks with the double weakness) and Murkrow having Pursuit. However, a fully healed Golem or a Golem at high enough health should take a Pursuit and then OHKO Murkrow.
Rocket Executive battle #5 (Goldenrod Radio Tower): Everything crumbles to dust to Ground STAB, but bear in mind that Houndoom will deal a good amount of damage with Faint Attack. Heal up if you're in low health before that fight.
Suicune (Bell Tower, Crystal only): No. This is completely, utterly out of question.
Gym #8 - Clair (Blackthorn City, Dragon-type): Avoid this matchup in general, although it is possible for Golem to defeat one of her Dragonairs. The only one Golem is fit to fight is the one with Thunderbolt, so make sure that you confirm that it has Thunderbolt before you switch in on it. Her lead has Surf, and another one has Ice Beam. Stay far, far away from Kingdra.
Rival (Victory Road): Same as last time, really. His team is substantially unchanged.
Elite Four Will (Indigo Plateau, Psychic-type): Avoid this matchup. Golem has very low Special Defense, and Psychic from one of Will's powerful Psychic-types will probably net a 2HKO. Don't try to set up a Rollout chain, as it will almost definitely be the death of your Golem.
Elite Four Koga (Indigo Plateau, Poison-type): As long as you don't get haxed really badly by Double Team and whatnot, Golem should be able to solo this fight. Ariados, his lead, has Giga Drain, though, so be very, very careful (or just avoid it). Don't risk Rock Throw's shaky accuracy; go straight for the Earthquake. STAB super-effective Rock Throw has the same power as neutral STAB Earthquake. Forretress falls to a few Earthquakes and can't really do anything to you in return, Muk is annoying with Minimize but should probably fall to a single Earthquake, Crobat might try to hax you with Double Team and Toxic but should die to two Rock Throws, and just handle Venomoth the same way you handled Ariados. It has Psychic, but it's not STAB and it's only coming off of a base 90 Special Attack stat, so there's really not much to be scared of.
Elite Four Bruno (Indigo Plateau, Fighting-type): Stay ouuuuuut. Well, actually, you can beat Hitmontop by spamming Earthquake, since its only real way of hitting you is by using Dig, and you can beat Onix by spamming Earthquake as well. Hitmonchan is sort of a gray area; it should go down to two Earthquakes, but it has STAB super-effective Mach Punch that might 2HKO if it gets a crit each time.
Elite Four Karen (Indigo Plateau, Dark-type): Avoid Vileplume, and WATCH OUT FOR GENGAR'S DESTINY BOND. You can OHKO Houndoom with Earthquake, but it will take a sizable chunk of your HP away with Crunch. Murkrow is easy to beat, but Umbreon is just the opposite; it probably will be able to take two or three Earthquakes before going down.
Champion Lance (Indigo Plateau, Flying-type): You can beat the Aerodactyl and the Charizard handily with Golem, but stay away from everything else. Gyarados is a no-go as it has Surf, the Level 50 Dragonite can nail you with a specially-based Outrage (remember, this is before the physical/special split, so all Dragon-type moves are special), and one of the Level 47 Dragonites has Blizzard, so you probably don't want to take that chance.
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, Golem is very slow and unlikely to outspeed anything but Graveler. As a safety measure, it is much better to not have Golem fight here at all.
Rival (Mt. Moon, optional): Alakazam needs to be avoided, it's fast and hits strongly for Golem's poor Special Defense. Gengar having evolved doesn't mean much of anything, instead. As usual, anything Grass or Water is out of Golem's league, while the rest is perfectly manageable.
Gym #10 - Misty (Cerulean City, Water-type): Everything is Water and... everything hurts. Don't do this to your Golem.
Gym #12 - Erika (Celadon City, Grass-type): Again, don't do this to your Golem. Her team may be laughable, but for something with a double weakness to Grass, it's really not. Use a better Pokémon here.
Gym #13 - Janine (Fuchsia City, Poison-type): Everything falls to Earthquake or, in Crobat's case, Rock Throw or Rollout. They're so underleveled that even using Rollout will cause literally zero problems. Don't worry about it.
Gym #14 - Sabrina (Saffron City, Psychic-type): Mr. Mime is doable, but both Espeon and Alakazam have a really strong special offensive and are extremely fast compared to Golem. You should not fight anything but Mr. Mime here, as it could be very dangerous.
Gym #15 - Blaine (Seafoam Islands, Fire-type): More Earthquake, more GG!
Gym #16 - Blue (Viridian City): Pidgeot fears Rock Throw, and Arcanine can do nothing against Earthquake. Alakazam, much like Sabrina's, is too strong; don't fight it. Rhydon is also stronger than Golem, so you can either OHKO it or be OHKOed by it, but given its double weaknesses, it's probably not worth the risk. Exeggutor's only threatening move is SolarBeam, so you can try to damage it until it either sets up Sunny Day or absorbs sunlight, at which point get Golem the hell out of the battlefield. Gyarados has Hydro Pump, avoid at all costs.
Rival (Indigo Plateau, optional): Golbat is now a Crobat. Big deal. Apply the same reasoning as last time.
Red (Mt. Silver): You can use Pikachu as set-up fodder, which is a godsend if you are allowing X items. Even if you're not, Golem still beats half of Red's team easily. It only needs to steer clear of Venusaur and Blastoise at all costs, and Espeon is best left to a teammate too, since its Psychic hits like bricks.
Geodude learns Rock Throw at level 11, which it uses to decimate the first two gyms. Then, it learns Magnitude at level 16, which annihilates any Electric, Poison, or Fire-type, as well as weaksauce 'mons in general. Geodude also gets access to the great Defense Curl + Rollout combo via TM04, or level 34. Also, Golem learns Earthquake at level 41, just in time for the Elite Four. And it that weren't enough, Geodude has access to a handful of out-of-battle moves in Headbutt, Rock Smash, and Strength. Another move worth mentioning is DynamicPunch, optimal with X Accuracy support and which provides good coverage.
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 Ratings
At what point in the game should I be evolved? Before Morty, preferably. If you can trade to get a Golem, do so as soon as possible. If you can't, well, Graveler's still really good, and is still a very solid Pokémon to have on your final team.
How good is the Geodude line in a Nuzlocke? Geodude is really, really, really good. Just the fact that it can manhandle basically the entire early-game puts Geodude on the very top of the GSC viability list. As long as you don't let it get hit by any Water or Grass type moves (or Ice, for that matter), you have yourself one of the best in-game tanks that Pokémon has ever seen.
Weaknesses: Ground, Steel, Ice, Fighting, Grass (x4), Water (x4)
Resistances: Flying, Normal, Fire, Rock, Poison (x0.25)