The photos were snapped July 26 in the Santa Monica Mountains, which was roamed by grizzly bears two centuries ago, the agency said in a statement.
The black bear likely came from the Santa Susana Mountains or the San Gabriel Mountains, both of which are known to have bear populations, said Joanne Moriarty, a wildlife ecologist with the Park Service.
The animal "may have traveled down through the Simi Hills and across the 101 (Freeway) in that area," Moriarty added.
A wildlife crossing had previously been proposed for nearby Agoura Hills "after research on local wildlife has indicated the need for habitat connectivity between the Santa Monica Mountains and open space to the north," according to the news release.
A black bear was killed in 2014 on a 101 Freeway off-ramp in Westlake Village.
"We know there's not a lot of connectivity there, and it is a problem for many of the wildlife species in the area," Moriarty said.