A grass fire that burned four acres near Yellowstone National Park's North Entrance is under investigation.

Park officials say the fire, which was just inside the park, was caused by humans.

Fire crews responded to an area between the North Entrance Station and Gardner River at roughly 6 p.m. Friday, according to a press release. When they arrived, a fire was spreading through grass and sagebrush.

North Entrance Road was closed for 90 minutes as firefighters extinguished the blaze.

No buildings were damaged nor park visitors injured thanks to firefighters' quick response.

Anyone who was in the area at the time of the fire and has information is asked to call the park's 24-hour tip line at 307-344-2132. Callers can remain anonymous.