When is the collective noun ridge used?

"Ridge" isn't generally used as a collective noun. Collective nouns refer to groups of people, animals, or things.

For example, you might say:

* A flock of birds (birds)

* A herd of cows (cows)

* A pack of wolves (wolves)

Ridge refers to a long, narrow elevation of land.

However, you could use "ridge" in a collective sense if you were referring to a specific type of feature that forms a ridge:

* A ridge of mountains (mountains)

* A ridge of sand dunes (sand dunes)

In these cases, the word "ridge" is acting as a descriptor rather than a collective noun.