Cloch is the Irish (Gaelic) word for a stone or rock. Clochán is a derivative of this, and there are plenty of rocks around Clifden in Connemara.

Drioch is not a word I'm familiar with, but I'm sure someone will be along with a translation. The original Gaelic name would probably have been Cóbh na nDroich Clocháin. There is no V in the gaelic alphabet. The n is put before the D in Drioch following a vowel to make the word (allegedly) easier to pronounce.

Come to think of it this may be an old spelling of the word Droch which means bad, so the translation could be the Cove of the Bad Rocks.

It would be very difficult to explain in text what the nD sounds like, but think of the knights who say "nih" in Monty Python and the Holy Grail and you won't be too far wrong!