A fast-moving wildfire destroyed a historic lodge and dozens of other structures on the Grand Canyon’s North Rim, forcing officials to close access to that area for the season, the park said Sunday.

The inner canyon, including Phantom Ranch, was closed, as were trails to the inner canyon, because a water treatment facility on the North Rim was damaged by fire and was leaking chlorine gas, park officials said. Chlorine gas is toxic and is heavier than air, meaning it could settle into the lower part of the canyon.

The fire destroyed 50-80 structures at the North Rim, including a water treatment facility causing a chlorine gas leak.