tilt back and up on a pivot

[imchongjun]

Hello, teachers.
Would you help me to understand what has happend to the rock in the following passage?

(Janet is trying to find a secret chamber behind the rocky slope)
And then, when she got there, she found she wasn't any place. The spot looked just like the rest of the slope even more so. There was brush, and there was rock, and that was all.
.......
Janet whirled around. A stunted bush that was like any other bush and the rock under it that was like any other rock had turned out to be something entirely different. The rock had tilted back and up on a pivot, and the shadowed, thin face and liquidly dark eyes of the man who was sometimes Tio Riquez and other times Bautiste Bonofile looked out of the black, square hole underneath it.

I do not understand "the rock had tilted back and up on a pivot" part. It seems to me that the rock first moved backward from the surface and then moved upward by some mechanical devise, but I have a strong feeling that my interpretation is wrong. I appreciate it very much if you could explain this sentence. Thank you in advance.

[archfiends]

Hello, teachers.
Would you help me to understand what has happend to the rock in the following passage?

(Janet is trying to find a secret chamber behind the rocky slope)
And then, when she got there, she found she wasn't any place. The spot looked just like the rest of the slope even more so. There was brush, and there was rock, and that was all.
.......
Janet whirled around. A stunted bush that was like any other bush and the rock under it that was like any other rock had turned out to be something entirely different. The rock had tilted back and up on a pivot, and the shadowed, thin face and liquidly dark eyes of the man who was sometimes Tio Riquez and other times Bautiste Bonofile looked out of the black, square hole underneath it.

I do not understand "the rock had tilted back and up on a pivot" part. It seems to me that the rock first moved backward from the surface and then moved upward by some mechanical devise, but I have a strong feeling that my interpretation is wrong. I appreciate it very much if you could explain this sentence. Thank you in advance.

It seems to me that the one side of the rock had been raised up, and then hold on a pivot.

[Rusty]

Hello, teachers.
Would you help me to understand what has happend to the rock in the following passage?

(Janet is trying to find a secret chamber behind the rocky slope)
And then, when she got there, she found she wasn't any place. The spot looked just like the rest of the slope even more so. There was brush, and there was rock, and that was all.
.......
Janet whirled around. A stunted bush that was like any other bush and the rock under it that was like any other rock had turned out to be something entirely different. The rock had tilted back and up on a pivot, and the shadowed, thin face and liquidly dark eyes of the man who was sometimes Tio Riquez and other times Bautiste Bonofile looked out of the black, square hole underneath it.

I do not understand "the rock had tilted back and up on a pivot" part. It seems to me that the rock first moved backward from the surface and then moved upward by some mechanical devise, but I have a strong feeling that my interpretation is wrong. I appreciate it very much if you could explain this sentence. Thank you in advance.
Here's how I picture it:
Tilt back and up is the same motion as an opening trapdoor.
A pivot is a point or short shaft on which something turns.
Put these two ideas together and you have a rock that sits on a pivot and tilts like a trapdoor.

[imchongjun]

Thank you, Archfiend and Rusty, for your comments. So the rock has been raised up! I got it. Thank you so much.