*!*!*! part 1
well first off you must beat the elite four and to have both of them you must have emerald
if you meet the requirements then its pretty simple
first off you must go to the weather station were you got your castform"
and on the second floor the person to the far left will talk to you
and tell you there have been droughts in area ###-could be 1 of 4 areas
once he tells you this you go to that area go inside the cave keep goin down
and you should see groudan now save 

!*!*!  part 2
catching groudan guide 
to catch groudon i suggest you first do a small amount of damage then
he will usually use random attacks 
wait until he goes to sleep and once hes asleep i suggest you get him to low hp
useing a water/grass attack,solarbeam would work.
once hes at red/yellow and sleeping throw a ultra ball and if he wakes up just repeat
until you catch him


*!*!*! part 3

now you go back to the weather station and he will tell you its been raining on route ###
again 1 of 4 go to the route and use dive until you find the right cave
go in and then you could repeat the same stradegy with groudan except if you get him to
red
and he wakes up and uses double edge your screwed so keep it at yellow


END of guide :D