You suddenly come to a small cliff. Fortunately, you are able to stop in time. Judging from the hoof-sized divets carved into the soft ground which go all the way to the edge, though, someone before you was not so fortunate. The cliff is oddly fairly short, with a much gentler slope to the west.

Misty is lying at the bottom of the cliff, about seven meters below. Some bushes seem to have broken her fall, but she isn't visibly moving.

(Misty is injured with broken forelegs and a broken rib; Eagle Eyes will want to have the Farm trail leader bring her back (she is a pegasus). Misty can be roused by Discolor and talk to Akasha.

The cliff is very steep. In fact, it's a concrete wall, mostly buried in countless years of windblown dust, in which plants grew and decayed to soil. There are louvers high on the wall.

At the base of the cliff, about 10 meters south from the bottom, there is a row of deteriorated concrete pillars about 30 cm diameter sticking out of the ground.

The pillar has a horizontal hole in it. The ends of the hole point to the other pillars in the row. There are red-brown stains on the hole and down the side of the pillar. It is otherwise uninteresting.

(If one digs a little, they will expose a concrete road on the side of the pillars nearer the cliff base, and find just more dirt on the other side (where there was water previously.)

--

A bit east and south of the pillars, there is a patch of unusually verdant vegetation on a hillside.

The cave is in this patch. There is a trickle of water emerging from the cave, which seems to be providing this patch with more water than the rest of the area.

The cave is actually a large concrete pipe. An adult pony could move into the entrance of it it by crawling only, but the depth of the dirt on the bottom gradually falls.

The pipe has a little bit of cool water at the bottom.

--

The pipe ends in a chamber with a sharp upturn. There is some sort of huge, silvery and rounded cone in the middle of the chamber; higher up it has giant curved fins protruding from it. Water trickles down the walls. The floor is covered with debris, including large pieces of curved, rusting metal.

The casing of the turbine was not as successful at resisting centuries of decay. It has cracks and holes. None are pony-sized, but they could easily be enlarged.

Should the party enter the penstock (a tunnel higher up, leading away), they will find it inclined upward with a small volume of water running along the ground, which has worn a slight groove in the cement concrete pipe, exposing pebbles of larger aggregate. You come to a huge metal wall obstructing further progress. Tiny jets of water shoot out from pinholes in the wall, the source of the water feeding the trickle in the pipe and ultimately the tiny "oasis" outside.

--

Powerhouse:

West: Backup generators. Up stairs, East: Control room, office, office, reception area (south) break room (it and the hall are collapsed, filled with dirt and debris, preventing further exploration.) Papers and wooden objects have crumbled to dust.

An engraved sign on the office: BOUNDARY LAYER, P.E. / CHIEF ENGINEER, WESTYORE HYDROELECTRIC DAM

The desk is empty of everything but a few trivial artifacts - paperclips, a chewed pencap, a bent tack and a long knifish thing that is not very sharp and had fallen into a crack in the desk. Either the user cleaned out the desk fairly well before he left, or other looters have preceded you here.

Other office door: ICE PHASE, M.V. / DEPUTY ALCHEMIST, NICKERBY COUNTY FLOOD CONTROL DISTRICT

This office was also cleaned out pretty well, but if someone looks carefully through the piles of decayed wood and rusted metal, she may find some enchanted glassware (for durability) that was accidentally left behind.

Dam / powerhouse
Underwater Ruins

Combat: Two Steps / Archangel / 23 Sanctuary is Lost

On the other side of the dam it's quite overgrown, but interrogating the locals will reveal that there is a local spring (a hint can be dropped with bystanders if necessary)


There are naught but a few concrete bits poking up from the ground, although those with local knowledge (kids) here would know the location of a "really straight cliff" that more educated may know is a ruin. 
There are some air vents at the top of this cliff that can be infiltrated. Alternately, they may find the "cave" in the hill. The cave leaks water, and is actually part of the outlet works. The two turbines are rusted and falling apart, and one can exit through their housings (in similar condition) to the interior of the building, ending up in the powerhouse. Their magical preservation was defective.

There are stairs up to an office and control room in the powerhouse. The control room has better ragnarok proofing, but there is still no electricity. T
Another side room of the powerhouse has oil generators. This is the room with vents that is still exposed. The preservation enchantments still work and they can be activated. There is a breaker panel here
with tweleve  breakers, labeled:

SERVO 1-6, CONTROL ROOM, HOUSE, EXCITER 1, EXCITER 2, PENSTOCK 1-2

Lighting/domestic power (HOUSE) or the exciters, and gates 1, 3, 4 will immediately blow. The other gates 2,5,6, work, and unless the controls in the control room
have been adjusted, will promptly open the intake. The remains of the turbines will be obliterated by this, allowing water into the powerhouse. (Much of it will flow out the outlet works of course)
This will spill the TE somewhere out into the old riverbed...

There is a FLUME HORROR in the powerhouse near the stairs to the control room. There is a good chance of somepony being exposed to the spores. 
There is a flume horror here. A giant amphibious anemone-like creature with tentacles and bulbous protrusions. Beware its deadly spores!