Signs of black bears have been found at the 110-acre park off Signal View Drive.
"This is the fourth year in a row that staff has noted some scat and some marking on trees indicating a bear has passed through," Manassas Park City Manager Jim Zumwalt told NBC Washington's Julie Carey.
Bears will scrape the outer bark off of trees in search of grubs, evidence they have found around the park, park officials said. The animals will wander across 100 miles or more, rangers said, staying in one place for two to three weeks at a time.
The trail's back loop is closed, and officials from the Department of Parks and Recreation are urging extra caution in the part of the park that is open.
Visitors with dogs should keep them on the leash. Trash should be put in the provided bins to keep bears from being attracted to the area.
Visitors who encounter bears should not approach them. Making loud noises such as clapping or sounding a car horn can scare them away. Experts also advise against running but say speaking will help bears identify humans and give them the opportunity to take a detour, Carey reported.
Across Virginia, bear sightings are on the rise. If you see a bear, you should call officials at 703-335-8872. More tips on black bears are available at the Virginia Department of Game and Inland Fisheries website.