I don't think you can get regirock in pokemon ruby.
There is no jirachi's cave.
Beat the elite four the cave should open.
You must has a pokemon had a Rock Smash.You go to Desert Ruins and go to a cave does open when you go to Pacificlog and go to a some earthquake and go again there the cave is open,Go enter, Read the text Go down 2 and go right 2 ,...
To open the Cave of Origin in Pokémon Emerald, you must first go underwater to the Seafloor Cavern. There you must defeat Archie.
that cave will open after beating the elite four near route 111
It's different in different versions.
In order to open the Regis caves in Pokemon Emerald you first have to go to route 134 and dive into the cave. When you are in there use dig. The first Regi cave is located in the desert.
This is because you have to go in the cave at the top of the town then the gym will open.
I don't think you can, in emerald you need the nationaldex and POW! it's open but in ruby and sapphire you can't.
sorry but you can't find it in Pokemon diamond/pearl without migrating regirock from Pokemon ruby, sapphire, or emerald. But I think there is a cheat on the action replay for it, but I don't know the cheat.
In Pokémon Emerald you can find Regirock within a cave that appears in the desert area however the sealed entrance to Regirock's cave inside the cave will not open until you read the braille inscription and then you go two steps left and then two steps down and then use the Rock Smash HM and then you will be able to encounter a Level 40 Regirock, you can find Regice within a cave in Route 105 however the seal on the cave within the cave will not be broken until you have read the inscription and then do a clockwise lap of the cave while staying next to the walls at all times and once you have accomplished this then you will be able to encounter a Level 40 Regice and then you'll find Registeel inside a cave in Routte 120 at which point you will need to read the inscription and then you will need to go to the literal middle of the room and then you'll need to use the Flash HM and the seal will be broken and you will be able to encounter a Level40 Registeel.