The slot canyons are made of sandstone. The slot canyons can be very dangerous.
People die in the slot canyons when water far upstream occurs. A cloudburst of rain can cause a wall of water to rush through the slot canyons, and it does happen.
A large area on the surface that receives rain can mean that all of the water will flow through the slot canyon like a funnel.
There is no advance warning so you really have to pay attention to the weather and the surrounding area and conditions before going into the slot canyons.