Head out of this area through the metal door, and go back to the fuel depot. Now that you're there, look in the garage at the wall with the license plates. Look at the one with the state that was under the compass, and make a mental note. Mine said "CLU-287", but this can vary as well.
License plate cheat sheet:
Head towards the generator, then the building behind it. Keep walking through this area until you get to the fork and take the left under the stone arch. Continue walking through this area, and go through the purple portal.
Cross back over the dam wall, and get to the elevator set into the mountain.
Enter what you saw on your license plate, and this should trigger power to the elevator. If like me you had letters in your code, they transfer like this:
A, B, C = 2
D, E, F = 3
G, H, I = 4
J, K, L = 5
M, N, O = 6
P, R, S = 7
T, U, V = 8
W, X, Y = 9
Z = 0
So for my clue, CLU-287, my number ended up being 258287. The numbers are arranged via a rotary dial, which for those too young to know that pattern, it goes counter-clockwise starting from 1 at the top right to 0 at the bottom right. The phone booth just outside the gas station will also show you which number corresponds to which letters inside of it's old fashioned rotary dial.
This will enable the elevator. Take it all the way down to the basement to find a new living space. Read the paper in here, making careful note of the numbers, as they will fill you in on data for a puzzle later. Go to the crank at the far end of the room, and crank it down - this will open a door up above.
Go back to the elevator, go up a level, and out the door. You will now see The Tree revealed in all its glory.