In this image, the green line is north. Those pink boxes are supposedly river objects, but to me they look like Bakers that outline the various mountain ranges in this level. Additionally, the blue box in the left corner is apparently the area where the player was meant to start the level.
I just did a quick and dirty import of a number of objects from the Plains level into my complete Isla Sorna terrain, and the results contradict what I'd previously thought about the plains. It seems that the area is further north than I'd thought. The blue box is situated at the end of the mountain range on the east side of the town, which runs roughly all the way to the ocean. If Anne were meant to leave the Southern Gate of the Town, she would go down a long valley before coming to the ocean. This is mentioned in the walkthrough:
Anne will have to find some other way to get to the plains, so she sets out in the only direction available: east towards the sea.
However, it also contradicts other facts in the walkthrough, specifically the ones that point to the intended exit direction being the Eastern Gate instead (the one you usually exit the Town from), since the prior area of text says this:
This is undoubtedly the valley that leads to the Dam in Retail. But if the starting area of PL was supposed to be up by the coast where the box is, that would mean the player would have to exit IT through the Southern Gate. Very strange. It seems by reading this that the player would have entered the same area that they do in retail, but the washouts on the road would extend into streambeds which would in turn prevent them from reaching the Dam. The quoteOnce outside the town, the player finds herself on the North Road, which leads through to the laboratory facilities eventually. This road ascends a steep ridge almost immediately, but whatever cut-rate engineer Hammond hired to build this road managed instead to create a convenient run-off sluice for the rainy season. What used to be a nice, gently-sloped road has washed out down its entire length, becoming a series of ledges connected by streambeds, completely unclimbable. (alternate solution: the road has a bridge to allow passage up a cliff, but the bridge is wrecked).
clearly indicates that you would then have had to go East, but in retail this direction is blocked by a steep cliff that looks like it wasn't originally intended to be there. This would have led the player down a valley between the mountains east of the Town (seen as the pink boxes on the left of the first image) and the mountains east of the Dam (seen as the pink boxes in the center of the first image) to the seaside, and east to where the blue box is. Now, there are two possibilities here:Anne will have to find some other way to get to the plains, so she sets out in the only direction available: east towards the sea.
1. The player left the Southern Gate of the Town, followed a valley east to the ocean, jumped along the coast and began PL where the blue box is located, which in turn means the entire area between the Eastern Gate and the Dam was the Plains, and that the open area between the central and right pink box lines was a second, more heavily-forested area of the Plains. This makes sense because that would mean the Dam valley with the North Road would be accessible from the start of PL, but contradicts the walkthrough saying the player exits through the East Gate...which means that at one point it is possible that the East Gate was actually the South Gate.
2. The player left the Eastern Gate of the Town directly into the Dam valley, then turned East past the T-rexes into a valley, which led to the ocean, jumped along the coast and ended up in a smaller Plains area, which is the area between the right-most line of pink boxes and the central one - this situates the Plains between Mount Watson and the mountains in the center, to the direct east of the Dam. However, this would prevent players from even reaching the Dam at all. This is more accurate to the walkthrough, but makes less sense terrain-wise.
Either way, the player definitely enters the Plains from the east, by the coast.Cliffside puzzle
After paralleling the ridge for a few hundred meters, Anne comes across some cliffs at the seaside, where the ridge runs out. Anne must proceed around the end of the cliff , hopping down from tiny ledge to tiny ledge, all the while 12 meters above the rocky coast. Once she has completed this section, by making one last drop, further than she can jump back up, she has entered the plains area.
Obvious enough - this is the area between the Dam and the start of PL. If she can make out the Dam in the distance, there is a possibility that the central pink line of boxes was indeed an actual streambed, and that the mountains to the east of the Dam were instead a stream (except for a small area where the Dam itself would be attached to cliffs - this area is the gap between the central pink boxes and the right-side pink boxes) as the mountains would obscure the view.Looking around, the player is presented with the grand vista of the plains. For more than a kilometer, open, short-grassed terrain dotted with occasional clumps of trees gently rolls off into the distance. Brachiosaurs are visible in the extreme distance, grazing on the few trees, and nearby a stegosaurus family and a pair of triceratops drink from the same. The land gently slopes up, and Anne might just be able to make out a vast gray concrete structure in the distance - the dam to which she must eventually travel.
Could THIS be the Eastern Gate that you exit the Town from..? If so, that would clear up everything and determine that the Eastern Gate is indeed the Southern Gate in actuality.Gate to Town
The road that used to run to the town is blocked by a gate. The gate includes a sign that reads, "Warning! Remote-operated gate system. Have your signal ready." On the ground nearby is a remote-control signaller, a small box with a space for a battery. The battery in it is corroded-looking and plainly non-functional..
This is present in the Plains level we have. It's north of the central pink box line, which lines up with its description in the walkthrough.*Blockhouse
a small cement structure in the extreme north of the plains, contains some items which hint at some sort of story: a child's toy, some dishes, a weapon.
Very little information on any of this, though the Rex encounter could potentially be the same spot as you encounter the pair of them in retail IT.*Crashed plane
(to the north, near the shore, has guns, some sort of physical puzzle to get up inside, whole thing unbalanced?)
*T-Rex encounter
(evade a T-Rex near the downed radio tower? Make him chase you into a pack of stegs/trikes?)
No idea where this is supposed to be...perhaps one of the large patches of black squares (sand terrain)?*Watering hole
A pond between two small ridges is one of the largest watering holes in the area. This is a good place for Anne to look for a dinosaur with a tag, and a good place to make dinosaurs have staged fights, or to menace Anne when she tries to get in close enough to grab a tag or attack a tagged dino.
The walkthrough mentions the Dam area itself at the end of a valley, which is the same as the one in B116, but it is fenced off and must be opened with some kind of opener, which has to be battery-powered from a radio collar seemingly attached to a larger boss albertosaurus. Oddly, the walkthrough also says the the stairs to the top of the Dam are on the WEST side, not the east side as they are in Retail, though to me this seems like it might just be an error on their part as everything else lines up correctly.
I'd also like to note that many of the objects in the Plains level we have are anywhere near the correct level of the terrain. If you were to raise the ground up to these object's height, the Plains would be about halfway as high up as Mount Watson's summit. What's strange though is that other objects line up almost perfectly with hills and ridges in places. It seems as if the entire island could have been at a higher elevation at some point, but considering the differences in coastal height between versions, you never know.Dam gate
The dam fills up the end of a valley up which the North Road runs. Anne is forced down to the valley floor by a washout on the road, if she has been following it up to now, and in order to get back up to the top, she has to get into the dam area, by using her gate opener-with-battery.
So that's all of the information I've gathered so far. Anything else would be of use so that we can assemble a collection of knowledge about this level as it is the only one we so far have no versions of at all.
, though it still seems weird that if visitors were to come through the west gate that the town is facing the north. 
I think reading this could somewhat help solve some more mysteries surrounding PL.
I took a look at them and it turns out I DO have these somewhere on my computer, just can't remember where. Either way, it doesn't really seem they reveal much we didn't know about Plains already.
. According to the file properties this was made on 3/31/1998. But the walkthrough was made on 6/27/1997 and was modified 8/15/1997.
