Oreads are to mountains what Dryads are to forests.
It's kind of fun to look at the wikipedia article on "nymphs"
, as Greek Mythology is chock full
of these kind of nature spirits. Fountain nymphs! Ivy nymphs! Honey Bees nymphs! Kind of makes you wonder about razorvine nymphs or portal nymphs or such, for a more planescapey feel. Hmmm.
Anyway. Oreads have the predictable spell-like abilities (stone shape, stone tell, stoneskin, meld with stone), and one less predictable one called "song of stone", which magically charms anyone who hears it (and fails a saving throw) for a year, requiring unusually strong magic (limited wish or holy word) to break.
There's also "snowhairs", old and powerful Oreads who have cut ties to individual mountains and protect entire ranges. They pack a bit more of a punch, including spelllike abilities such as earthquake, animate rock, part stone, and a petrifying touch that turns people into boulders (requiring both stone shape and stone to flesh to fix).
* An Oread's pet snow leopard has wandered off, and she can't leave the mountain to go find it. She'd be very grateful to any adventurers who could find and retrieve him, although the favor of an Oread is a somewhat tricky to cash in, it'd definitely be a nice thing to do.
* "Unlike dryads, [oreads] are not vulnerable to the death of their mountain - after all, a mountain cannot die - but they are pained by mining, deforestation, and magical erosion." A Doomguard factotum, seeking to gain prestige and influence with his faction, decides to really test that "mountains cannot die" theory, hiring a slew of talented elementalists and a small clan of dwarven miners to get to work. The PCs might get hired as well and have to defend the miners from an increasing angry Oread (if not the local snowhair when things progress), or they might decide to come to the Oread's assistance, depending on their proclivities.
* The Greater Titans have hatched a cunning plan to assassinate the seven snowhair oreads that guard Mount Olympus. The Greek Gods could fix the problem themselves, but they'd also probably show favor to any mortal who solved it for them. Of course, the snowhairs have important jobs to do and aren't going to all sit cowering in a cave: the PCs will probably be stretched pretty thin protecting them as they go about their mountain-range-spanning business.