Visitors to the Grand Canyon might notice an unusual smell this summer — that of burning rubber. It’s so hot within the walls of the Grand Canyon that the National Weather Service has issued an Excessive Heat Warning below 4,000 feet, comprising the inner parts of the canyon. The extreme heat could cause parts of shoes and hiking boots to melt, ruining not only your day of hiking but also your gear.

Within the canyon walls, the heat is amplified because as air sinks, it becomes compressed and releases heat as energy. That heat radiates throughout the canyon, raising ground temperatures above what’s found on the canyon’s rims. Day-trippers and backpackers are advised to be mindful of their footwear, as the extreme heat could cause shoe soles to separate from the rest of the shoe. Visitors should also pay close attention to their travel companions. Asphalt may be too hot for dogs’ paws, resulting in burns to their foot pads.

Park rangers encourage visitors planning to hike down into the canyon to do so before 10:00 AM and after 4:00 PM, in order to avoid the hottest parts of the day. Hikers should bring and consume plenty of water and be mindful of their physical abilities (keeping in mind that once someone goes down, they must also climb back up again). In such an extreme environment, there’s no shame in taking a break under the shade of the canyon walls or a tree. The National Park Service also offers canyon-specific hiking tips on its website.