Final answer:
Two plates collided to form a convergent plate boundary, causing the bending and folding of rock layers, and the presence of a shell supports this theory.
Step-by-step explanation:
The description of bent and folded rock layers and the finding of a shell suggest that the area where Tina is hiking experienced tectonic forces, producing a convergent plate boundary. At a convergent plate boundary, two plates collide with each other, causing compression, folding, and uplift of the Earth's crust. This type of tectonic activity can lead to the formation of mountains and the deformation of rock layers.
Learn more about Plate Tectonics