YELLOWSTONE NATIONAL PARK, Wyo. (AP) — Two hikers were injured in a bear attack on a popular hiking trail near Yellowstone National Park’s Old Faithful geyser, park officials said Tuesday.

The attack was described by officials as a single event Monday afternoon along the Mystic Falls Trail.

A large area of the park near the Midway Geyser Basin was temporarily closed pending an investigation. The area includes at least five trails and several backcountry campsites.

Park officials said one or more bears were involved, but did not specify which species. The park has populations of both grizzly bears and black bears, which can be difficult to tell apart at times. Grizzlies can be more aggressive and they grow much larger — as much as twice as big as black bears. Black bears usually have darker coloring.