An unattended encampment may have sparked a fast-moving brush fire in Riverside that quickly grew to 70 acres and briefly prompted evacuations Thursday, authorities said.

The fire — which officials said was “human-caused, most probable due to an unattended encampment” — erupted in the Santa Ana River bottom off Grand and Rubidoux avenues shortly before 10 a.m., spurring the closure of the Santa Ana River trail between Ryan Bonaminio and Anza Narrows parks, Riverside Fire Capt. Brian Guzzetta said.

By 12:30 p.m., the size of the blaze was estimated at 7 to 10 acres. About an hour later, though, authorities reported a significant increase in activity. Flames had burned up to the backyards of several homes that overlook the river bottom, and firefighting efforts were hampered by a heavy cover of dry brush, Guzzetta said.

Authorities ordered the evacuation of about 25 homes along Old Ranch Road and Park Cliff Court and opened an evacuation center at a seniors center.


All evacuation orders were lifted about an hour later. Officials credited a shift in the winds and the arrival of mutual-aid firefighting resources, including aircraft.

The fire was holding at 70 acres and was 50% contained as of 8 p.m. Full containment is expected late Friday evening, fire officials said.

No structures were damaged, and no injuries were reported.