Flash Floods.
High water is a threat during the flash floods that may follow summer thunderstorms. You must be alert for this because a flash flood may travel down the watershed to you even though you were not rained on. Flash floods make roadway dips potential death traps. If you are caught in high water, drive slowly to avoid stalling your engine: Do not splash through at a high speed. And by all means, avoid any high water! Washouts are a hazard in a storm and afterwards, so be on the lookout for them. These same precautions about high water and low spots apply to camping, too. Do not camp in washes and arroyos. They could turn into swirling rivers while you sleep, and you might not even have the warning of raindrops to wake you.
Park Regulations
Driving.
The maximum speed on park roads is 72 kilometers (45 miles) per hour. Slower limits are posted; please observe them. Do not pass or park on curves, and take road dips slowly. Motorized vehicles are restricted to park roadways and are prohibited on all trails. Check with a park ranger before driving the primitive roads.
Trail Use.
Stay on trails because shortcuts mar the area and can cause erosion and destructive rockslides. Smoking is not allowed on trails because fire is a constant hazard here. Please carry out all your refuse.
Camping and Fires.
Camping is limited to campgrounds except for backcountry camping, which is by permit only. Building wood and ground fires is prohibited.