From Pathfinder #176: Lost Mammoth Valley, which isn't enabled.

Rockfall Ceiling

HAZARD 5

MECHANICAL

Stealth +10 (trained)

Description A load of rocks, held up by a rope pulley, is dropped on the cavern's lower level.

Disable DC 25 Thievery (trained) to pin the pulley in place

AC 22; Fort +15, Ref +15

Hardness 12, HP 50 (BT 25); Immunities critical hits, precision

Drop Rocks

Trigger A creature holding the rope pulley pulls it

Effect The net releases, dropping rocks on all creatures and objects in the lower half of area A15, dealing 4d8+14 bludgeoning damage (DC 26 basic Reflex). The area then becomes difficult terrain.

Pathfinder #176: Lost Mammoth ValleyOGL