Answer:
In classical physics, the attraction of gravity depends on the mass (weight) of the two objects (you and the earth) divided by the square of the distance between them. Thus you would weigh more in a valley (closer to the center of the earth) than you would on a mountain top (farther away)
One might want to argue that when you were in the valley, the mass of the mountains above you countered the pull of the earth, but I think this effect would be trivial