Wait do you mean ground type or rock type? Or dual ground/rock types? Either way here are some options
Rhyperior: Rhyperior, when it comes to defense and attack, is a beast. Despite having six weaknesses it can utilize the ability solid rock to tank supereffective hits, some even on the special side. It's special defense and speed are quite poor, but you team has some speed and can take most special attacks. A great offensive movepool including earthquake, stone edge, rock blast, aqua tail megahorn and the elemental punches make Rhyperior a great contribution to your team if you think you can handle its defensive weaknesses (especially water and grass) and work with its slow speed.
Rhydon: If your looking for some gen 1 nostalgia, here's your rhino. Although it may appear to be inferior to Rhyperior at first glance, eviolite levels the playing field, giving Rhydon greater bulk than its evolution at the price of less offensive potential. But don't be fooled. Rhydon is still the offensive monster it was in Gen 1, and possesses a great movepool practically identical to its gen 4 evo.
Nidoking/Nidoqueen: These guys are most likely your best best choices if you want a special attacker, with the only competition being Omaster, who'll compound Blastoise's weaknesses, and Tyranitar, who is awesome but will summon detrimental sand. Although their stats are somewhat lackluster, with their hidden ability sheer force they can become great offensive threats. Wielding earth power, sludge wave and a ridiculous amount of coverage, including thunderbolt, ice beam and flamethrower, they are both great offensive contributors. Choose Nidoking if you desire more power and Nidoqueen if bulk is more your style.
Garchomp: Garchomp has a well deserved reputation of being a powerhouse. Base 130 atk 102 speed and nearly unresisted coverage with STAB alone is the main reason. Throw on swords dance and you've got a sweeper, and fire fang/fire blast can remove any courageous ground-immune steel type that dares stand in its way. Surprisingly enough, Garchomp and Dragonite can actually compliment each other, as they can each draw out and remove steel and ice types that threaten them, allowing the other to sweep the opponent's team.
Aggron: Aggron looks, and is, scary. Base 180 def and 110 atk, a diverse movepool, and two double weaknesses makes it appear to be the Rock/Steel version of Rhyperior. What sets them apart? Two things. First, Dragonite resists or is immune to all of Aggron's weaknesses and vice versa, making a surprisingly decent core. Second, is a little breeding move by the name of Head Smash. Obtain a Rampardos, breed Head Smash onto an Aron egg, and now if that egg has Rock Head as it's ability, your future Aggron has a recoil free, drawback free, base 150 power STAB move. Add on a powerful STAB Heavy Slam, and great coverage in Earthquake, Aqua Tail, and the Elemental punches, and you have yourself one terror of a physical tank. Basically it has the same issues as Rhyperior. It is slow and has poor special defense, but this can be handled, and Aggron may run Rock Polish if you want it to solve its speed issue on its own.
There are many rock or ground Pokemon who help, so do not limit yourself to these suggestions. Hope this helps.